There is no telling what is causing the problem if you are using the Frontline, faithfully, but it sounds like you need to have your apartment professionally exterminated if you don't want to use a bomb. I haven't had to bomb in a long time, but when I did, it always worked. You just have to get any pets out of the home and allow it time to air out before you let them back in. Frontline is great, but it only kills the fleas when they bite the cat or dog, so getting the out of the carpet sounds like what you need to do.

Good luck!

Logan