I believe if you are having issues with pain and blisters/calluses which are believed to be caused by pitches ypo are supposed to pitch in the direction of the pain. You mentioned going to a reverse, but from your description of the problem that wiil do you no good b/c you with be reverse with impropel lateral pitch and you will most likely start to pinch/squeeze due to the reverse and begin to callus at the base of the thumb.
My advice would be to pitch the thumb in the direction of the pain, whether it be left,right,forward or back.