what is wrong with my shih tzu? licking his butt, belly and thighs....?

[rox]

I get his anal glands expressed about once a month. this weekend he started licking, so i took him to the only place open (pet smart) they express only externally and said he was full but they dd not get it all. On Monday, I took him to the VET. He expressed the glands internally. He said his glands may need to be removed or he has a tumor. he prescribed anti biotics. End of story. My boy came home, he got a bath and continues to lick excessively his belly, thighs, and butt. I also had him checked for worms. No worms.... I will call the VET tomorrow... I did not ask many questions because i assumed it was the glands again. What does everyone think? Any experience with this? It is so bad.... it gets him up from sleep to lick and his tongues has to hurt. what do you think it could be? he is 7ish yrs. old