Trying to strengthen upper back muscles using therabands due to having chronically overstretched muscles. they keep burning after exercise. any ideas?

Common: What you describe is common after exercise. Especially if the muscles are chronically overstretched. As you strengthen these muscles, often this can take several weeks to months you should see a decrease in the burning sensation. If it does not subside, then maybe have the sports med doc look into a nerve impingement as a source of this burning sensation.