Thanks for writing to H.C.M. for your query.
I have gone through your query regarding painful blister
behind the ear, though you had been operated for your jaw problem and in that surgery incision had been given in front of ear. You are confussed as this is related to operation, here I would like to tell you that incision was given in front of ear and this blister is behind the ear therefore they are not related to each other.
To get relief from blister you may take-
(b) Anti inflammatory.
(c) Antiseptic ointment over blister.
I hope this will help you.