Firstly, I'm so sorry you're going through so much pain.

I do think diagnosis is important because that will, to a large extent, determine your treatment. For example, if you have BPD, your treatment would be less about medications and more about controlling your mood lability and behavior with DBT. I strongly suggest you find your way to a psychiatrist so you can be evaluated.

I'm curious if your violent episodes are related in any way to (i.e. as a reaction to) any difficulties with relationships. This is a major feature of BPD (not necessarily violent reactions of course, but exaggerated ones). You say your episodes come out of nowhere, but I wonder if your therapist is concluding that they're coming from relationship issues.

Of course we can't diagnose you here, I'm just curious about the above. Could be BP, could be BPD. I hope you're able to find a psychiatrist and that you find peace.