My dog is always scratching but doesn't have fleas?

I have a 6 month old Siberian Husky who I've had since he was 7 weeks old. He had Roundworm and Fleas when I got him, but the vet took care of all that. He is up to date on all medicine and is healthy. The problem is that he's always scratching and biting himself. I look but never see fleas. When he gets really bad I give him a bath and that helps a little. My vet charges too much money just to see him and I can't afford it right now. Could it be a food allergy? I feed him Purina puppy chow, always have. Could he have dry skin? I see a little redness, but I don't if that's b/c of how bad he was biting/scratching himself. Thankyou.