Hi thanks for the query.
From the symptoms you had described it could most probably tenosynovitis
(Inflammation) of tendons of the thumb named scientifically as Dequervains tenosynovitis. I would advise you again consult the doctor who had given a cortisone
shot. You could have one more shot of injection and along with continuation of splint
, or prefer to go for small surgical procedure to release the tightened bands in the tendons.