Salmonella,
Fleas have an egg-larva-pupa-adult life cycle. If they get established in your house, the adults you see on your pets are only the tip of the iceberg. The eggs fall off the pets into the carpets and then hatch and go through the larva and pupa stages. To completely rid your home of an infestation, you have to break the lifecycle, meaning use a product (usually an IGR, insect growth regulator) to kill the eggs and larva in addition to something that kills adults. Some products do both and some are combinations of chemicals that will do both. Treating for the adults only with flea baths, dips, etc. that contain pyrethrins/pyrethroids, while very effective against adult insects, will NOT kill the eggs and break the cycle. That is the reason you are still seeing fleas even after multiple flea baths. Also there is a toxicity risk with pyrethrins/pyrethroids if used improperly and for sure don't use them on cats.
My advice to you is to quit dicking around with over the counter products and bite the bullet, spend the money, and go see your vet. They SHOULD have the latest products that are effective against the entire flea lifecycle. Keep in mind that, like Doc Paul said, you will need to treat all the pets in the house(dogs,cats,whatever)even if they don't go outside. This is something that will need to be treated for awhile until ALL the adults, larvae and eggs are killed. For serious infestations, you might need to fog the house as well. Simple frequent vacuuming can help manually remove egg/larva too. Just remember to change bags right away and dispose of the used bag outside of the house somehow. Treating the yard may be a possibility too. I don't know much about that, though. I have heard diatomaceous earth works for that but don't have any experience with environmental treatments for fleas.
Attacking the fleas on all fronts (pets, house, yard) is often required.
Good luck. Hope this helps. Flea infestations are miserable and take a serious effort to clear up.
Last edited by JayJunem; 05/26/17.
