Hi,
I've had similar issues for almost a year now with little to no pain relief. I don't think it was tendonitis though i think it is instability. I would try find a physio that is a good hand therapist and see one. I've been seeing one steady for a month or so now and he is working at mob'ing my carpals to break down some scar tissue that is between the carpals and part of a ligament.
I also have a small ganglion cyst somewhere in there that was revealed on Wikipedia reference-linkMRI (the MRI showed a TFCC tear but that is not the issue i am experiencing).

I would suggest and MRI and a good hand therapist.
Good luck!