By "stuff from the vet" I assume you mean Advantage? That product is usually pretty effective at stopping the flea cycle. Is it possible that the fleas are breeding in your carpet and jumping back onto your pets?
It makes a huge difference if you don't have carpeting. It will also make a difference if you keep your pets inside (not to mention cats kill a lot of native species and migratory songbirds). If your animals are running out and in, of course they will bring in fleas, and the fleas will reproduce like crazy in the carpet.
Planet Natural has some natural flea products. I'd ask a vet's opinion of the ingredients just to be safe. http://www.planetnatural.com/site/flea-carpet-powder.html
Once you get the carpet fleas under control, comb your pets with a fine-toothed comb every day or so. Crush the fleas you find, or drown them in rubbing alcohol.