I admire your detailed analysis of your struggle. It is clear you have a great deal of courage and persistence in looking for answers.
A diagnosis is only important if it helps generate a treatment. I wouldn’t focus so clearly on getting the diagnosis right. In fact, a diagnosis only looks at what is wrong. What it seems to me is that there are a great many things here that are right. I propose shifting your focus to them and changing your type of therapy to group. For your situation it is more dynamic, involves more feedback, and is much less expensive.
The group will shift your focus from self-reliance to learning to receive different types of feedback from others — and how to understand that extreme forms of empathy are just as debilitating as not having it. Solving problems for others isn’t the same as self-reflection and experimenting with how to solve your own can happen with a supportive therapy group. The ongoing process of a well-run therapy group will allow you to get direct feedback on your process of interacting with others in real time. Individual therapy traditionally doesn’t do this. (For more information on groups see my blog The Healing Crowd, at Psychology Today.