as I have tried to explain to MANY people.... you may NEVER see a flea.
(as for the woman that swore her cat didnt have fleas.... and out of no where... a flea dropped from the cat
onto the table!!!)
the allergy to a flea bite could the major issue.... I would do a topical flea treatment.... or you could purchase a Capstar ... kills ONLY the alive fleas but only is good for that day.
they do make a flea and tick pill you can get fromt he vet that is good for a month...
also you may want to look at a food allergy, seasonal allergy.... products you use in your household, laundry detergents you use...