OK - I have been there before. For me, it was getting my span and pitches just right in conjunction with cleaning-up my timing. My span was originally too long and my pitches were too steep. Not to mention, I was pulling the ball down, out of the swing and creating unneccesary friction(tissue damage) to my thumb.
I also went with less bevel in my thumb and experienced an increased relaxation in my grip. I never thought I would say this, but I add tape as I go each night.
Randy76