I agree with booktigger; this really is a matter for the vet. One of mine is allergic to flea bites, and has to see the dr. when a flea happens to find her. Just because you don't see many doesn't mean anything; one is all it takes.
If you've see even one, you can bet there are plenty more around. Flease usually will jump on the cat for a meal and jump off and live in your carpets. You need to deal with the flea issue both on and off the cat. If you do a search in this forum you will find plenty of information on how to get rid of fleas. There have been many, many threads dealing with this issue.
Definately sounds like a flea allergy. My one cat is allergic to flea bites and even if I look and look and don't see any one here, there is usually one lurking somewhere and that one will cause her whole neck and back break out in little scablike things.