I Have Been Giving My 13 Year Old Cat Flea Meds For 2 Months Now. I Don't See Any More Fleas But He Scratches All The Time. It's Like His Skin Itches. Any Idea?

Wondering if there is something i can do to stop my cat from itching? He has no fleas, I have given him 2 doses of flea meds. (front line).