GE,
I'm going thru tendonitius in my left hand,mostly thumb area. Very painful as you said. I played Fri. and Sat nights july thru aug. and now have some time off. My friend in the health field has been helping me out.Your therapist will lead you to the right outcome. Here's a couple things that are working for me . Cold pack right after direct use of left hand , followed by heat. 15-20 minutes each. Then repeat heat later. I also purchased an Ace brand Thumb Stabilizing brace. It keeps you from over working your thumb. I've also slowed down as much use of my left hand as possible. Mine is feeling much better in the last week. But as you were most likely told this can take a long time to heal. Advil was also advised if you can use it.
I hope this helps a little and good luck.
Joe
I guess one way to treat this is give your hands a little time to recover? Like maybe a month break? I did this and it's effective.