You'll have to bathe him w/a good flea shampoo and use a comb afterwards to get rid of the eggs, etc. caused by fleas. When you bathe him, the fleas will move to his head and you can easily get them off him w/the comb. The shot was probably Prednisolone which will help w/the itching but the fleas will still be there so there will still be irritation and scratching. The fleas can also make him very sick so it's important to get rid of them. Good luck.