I'm coming up on the seventh anniversary of my mTBI, so I know where you're coming from. Like you, my job is gone and my lifestyle has undergone a major downsizing. Like you, I also have times of deep, deep despair.
What I find helpful is to try not to think of it all at once. I try to identify one thing I might be able to change that would make things better. For me, recently, it was returning to this site and the support of people who understand.
In your case, it sounds like finding out about this burning sensation might get you back to a place where you could cope. Some of the others seem to have experience with this issue.
Like the others, I would also suggest trying to find a local support group. They are trying to organize a group in my rural area. I went to a meeting a couple weeks ago and meet some really great people. The sense of being understood and accepted was so refreshing. I often feel alone, but I'm not - and neither are you.
Hang in there. One day at a time.