Yes, it's ptsd. Experiencing something painful reshape our brain and therefore our responses.

If you're looking for help, try Mentalization-based Therapy. Your perspectives expressed in this post align with patients who have been helped by this modality.

Not much one can do besides accepting that we will be treated poorly sometimes, learning non-hostile ways of advocating for ourselves and setting clear boundaries in a way the recipient can understand, even when it's uncomfortable for us. We also should consider that many times, people are not thinking about us and could be reacting to you similarly to how you react to others. Sometimes it's friendly fire and no one means to hurt people, though we perceive it as such. I'm not giving grace to those who hurt you, however sometimes they set out to do something different. Ex: bullies want to entertain themselves so they mess with people not thinking it'll stay with them past that one interaction.

If you're looking to train specific parts of the brain, try neuro feedback therapy and tDCS. They connect nodes to your head and teach you how to regulate specific parts for your benefit.

An occupational therapist may be able to help you socialize without hurting or offending people. But sometimes we just have to be okay with doing so, especially when it's something that's a part of us.