Some people are more susceptible to flea bites than others. From experience it sounds like you have some of the little @^$#%^# in the house. In general the bites really show up within 24 hours of the attack and last for a few days.
Liz is right - keep on vaccuming the floors and emptying the bag outside after every use. When I had an infestation I sprayed lavender water all over the place - read somewhere that fleas are repelled by the stuff and I believe that rosemary can be effective as well.
The infestation I had came when I moved into a house whose previous occupants had a dog. I had no animals, but it took me a good two years, and a visit from the local councils pest remover to finally clear them out.