That happened when I broke my toe. What fixed it was gently pulling the toe out to pop like you would a knuckle that wasn't broken. I am sure it has to do with circulation.

Try pulling very gently. Not so it hurts more than the exercises. Also try squeezing a ball instead of just fist. Also try stretching the fingers the other way, bend back instead of forward.

A PT person will know a LOT more than the Dr about recovery.