My Cat Is Licking His Belly And It Is So

my cat is licking his belly and it is so red and very sore looking, he recently stopped going out doors on a regular basis, I believe something scared him about 6 or more weeks ago, and he supposedly had a abscess on his left hip the vet said and was on antibiotic for a week, any ideas of could it be cystitis? He doesn't seem to have a problem going so I am only guessing by reading things on the great old internet?