Just getting here after a rough day. Hopefully I'm coherent; apologies if I'm not.
First, anais.butterfly, I am very sorry for your difficult and painful day today.
Let me address one thing you said immediately. You said
I want to curl up in a ball, put my hands over my ears and scream until all of this goes away. And the thing is, it won't go away. I will be broken like this forever. Jeez, this happened when I was 3, I never had a chance to not be broken. The most I can hope for is that I find peace with it.
You are in the worst of it right now. Remembering these events you are also experiencing the emotions of that injured three-year old in an adult body and with an adult mind, that is often overwhelming. The emotions of a three-year old are more raw and often more intense than those of adults, but you are feeling them now, unfiltered, and that degree of rawness is unfamiliar to you, so it is likely frightening on top of being overwhelming.
But I want to be clear: You will
not be broken forever. You will always have that experience or those experiences in your history, but just like a broken bone heals to become stronger than the unbroken parts surrounding the area, you can heal and be stronger emotionally when you come out the other end with you working through these experiences.
If you don't mind, I would also like to reframe your experience for you with your returned memory and its timing. If you weren't triggered by something in your environment at work (which could have been anything, even things you might not register it as being the source). Your brain likely did not wait for you to get home for a reason. Despite it being terribly difficult for you to maintain yourself through your day as you said, getting the memory at work did a couple things for you. It provided you with a persistent distraction from the memory so you could not be as immediately consumed by it, by coming at a time where you knew you had certain things that needed to be done. Since you mentioned substance use in your post, it also came at a time where you had no access to such things, and could not get access to such things, until the memory had settled a bit. So, despite the difficulty from having the memory return while you were at work, your brain was working to protect you now, just as it worked to protect you when you were a child by hiding the memory in the first place.
I greatly applaud you not using substances to shut down the emotions when you got home! That is a very good job of taking care of yourself.

I have faith that healing from this will end it. I just want to be happy 
I am glad that you have that faith, because it is true, healing from this
will make it possible to feel happy again. Hang in there.
To answer assorted questions (and near-questions or potential questions) from various people:
Is it possible for memories from childhood (or later) to be repressed? Yes, in fact more than half of those traumatized in childhood 'forgot' (repressed) the memories for some duration between when the event or events happened and the age of about 40. [I believe that 40 was the oldest participant in the study, a study done entirely with participants who had third-party confirmation of the trauma, so there was confirmation of the traumatic event.]
Yes, it is good to get memories for traumatic experiences in childhood back. Why? Because the way you looked at yourself from that moment on - the way you interpreted
everything that happened to you and around you afterwards - likely originated with how you interpreted that traumatic event and what it 'meant' about you. [e.g. for physical abuse: possibly the idea someone was a 'bad' person and 'deserved' punishment; e.g. for sexual abuse: possibly the idea someone valuable only for their sexual functions; e.g. for neglect: possibly the idea someone is not worth being taken care of] It is much easier to undo those long-standing thinking patterns if one understands their source. It is possible without regaining the memories, but may not be terribly easy as there's no source one can point to and understand that interpretation's context. To understand that at the time the interpretation was made for that event that interpretation would have seemed reasonable based on the environment and developmental comprehension one had at that time. Understanding that, it is then easier to understand that that it is not an accurate representation of one's worth.
Is hypnotism a good method to regain memories? No. Simple as that. Hypnotism can help with many difficulties, but there are better and safer ways to regain memories (most come when the brain is in a place where it feels ready and safe enough to process them).
Since one is in a more suggestible state when hypnotized it is not a good idea for use with repressed memories. If the therapist is too 'pushy', then memories may surface before one is ready or equipped to deal with them. That doesn't happen with memories surfacing on their own.
If the therapist doing the hypnotism is 'looking' for repressed memories their subtle and not-so-subtle questions may induce memories of events that might not be accurate. Let me be clear: it is absolutely impossible to induce the intense horrific emotional state that accompanies actual traumatic events, and it is also impossible to induce a lifetime's adaptation to mistaken thinking about oneself that would come from a childhood trauma. In other words, a cognitive memory might be induced, but the emotions and other sequelae of such a trauma would not be present. [So the so-called 'false memory syndrome' that abusers and enablers promoted some years ago (with no research at all to support the 'syndrome') was pure bullshit.] Regardless of not being able to induce the emotions and after-effects of false memories, them being induced in hypnotized states would likely derail and delay the finding of the actual cause for difficulties presented. They may also confuse actual memories that might be similar, thereby making the abused question the reality of those actual memories, which would massively slow therapy.
I was starting to write a book to help those who had limited or no memories of their childhood to remember it or parts of it just prior to my first head injury (which derailed most functioning and left me with little mental capacity beyond work). I was finding resources to compile a questionnaire or list where each question or line was a different example of what a child's typical experience for each age range would be. The questions/items would include things like chores required when young, experiences with lost teeth, experiences starting school (and during it), and so forth. The idea was that one would read typical events in a child's life and try to remember their own related experiences. Often just reading of a similar event from childhood can be cueing enough to recall either a normal healthy experience, or to remember a disturbing traumatic one. A close-enough approximation to what I'd hoped to create might be to pick up a book on child-rearing aimed at specific age groups and think about how what is described in the same as, or differs from, what one experienced as a child. [There was a series of books I'd picked up as one resource. The one for the age you described, anais, is here:
Your Three-Year-Old: Friend or Enemy by Louise Bates Ames and Frances L. Ilg.] There was a whole series of these (clicking on the author's name on Amazon and then selecting "Visit Amazon's Louise Bates Ames page" can take you to the others).