Hiya! I'm having similar issues and there's another thread about flea problems.

Have copied this from the other thread (sorry for just copying the wording, no idea how to copy and paste posts from another thread) and have just ordered some myself for my furballs.

"I use Diatomaceous earth. Make sure it's the food grade stuff though.

It's natural, really cheap and completely harmless to pets, but to fleas it's like broken glass. It cuts them open and then dries them out, killing them within a few hours to a day or so.

A teaspoon's worth rubbed into my cats fur every couple of days for a couple of weeks rids her of all fleas."

Once the cat is flea-free, give it a couple of weeks, or whatever time your vet recommends, then get it a Program jab every 6 months. This doesn't kill fleas, but makes them infertile or something so stops them breeding. This worked beautifully for me in a multi-cat household for years. You just need to be as diligent about getting it done every 6 months. as you would with giving them their annual boosters.
No more chemical sprays or spot-ons needed!

I have used Advocat on my dog for years without any problems - and without encountering a single flea! But now she has a serious health condition and I'm a bit wary of using what is, after all, a systemic insecticide
A friend who used to work in a vets told me that vets tend to push the Advocat because it's more lucrative for them - I'm looking for a gentler alternative.