I have a 4 yr bull terrier,exhibiting strange behavior. He is gnashing and licking from side to side at his shoulders and fore leg- as if he is itching or being bitten by a bug etc. i am concerned as this continues non stop 12 +hrs. back and forth shoulder to shoulder. He has some sort of scab on his nose and i am wondering if an insect bite or tango with perhaps a possum could be making him have a toxic nerological behavior or perhaps have sarcoptic mites (the skin is normal except from his licking and drool) He is on antibioitics for the bite and prednisone for what the Vet thought was a grass allergy. I am not convinced -help!!!!

Optional Information:
Age: 4; Male; Breed: bull terrier

Already Tried:
soaps, cremes, prednisone, amitryptaline benadryl