What did you use for flea treatment, and how long did you use it? A proper flea treatment can take 3-6 months to completely get rid of all fleas in home and on pets. Home remedies and natural remedies rarely work. Use Frontline, Vectra 3D or Nexgard once a month for at least 6 months, and vacuum regularly (cleaning out canister or changing bag each time)
what was your flea treatment? Shampoos might kill what is harboring at that point and time, but not the next eggs that hatch an hour from now. I like frontline plus. Also there are pills from the vet you can obtain that will kill for at least 30 days, with frontline backup going forward. Some people prefer advantix. Or you could indeed have a food allergy. Can you still see fleas? Have you treated living quarters and yard?