I'm sorry to hear this, fleas are terribly tenacious. You have to be aggressive and consistent with your attack too.

My vet told me eons ago that the flea/tick drops/collars etc really don't do much as the life of the insect is short and they drop off or die before the commercial product really does anything.

You have to treat EVERYTHING on the same day: house, animals, yard, car, fabrics. There's no way around it. And then, you must do it within 5-6 weeks again (all of it) to kill the eggs hatching before they can reproduce.

We had a bad season down her years ago after a bad hurricane. I sent the dog to the groomers for the day and to be taken care of while I sprayed the yard (there are some good easy sprays that not only take care of the ticks/fleas but also the normal yard bugs) and washed all the rugs, bed linens etc and vacuumed and dusted and misted the drapes etc. I sprayed around the openings of the doorways and windows too. At 5 weeks, I did it again, and while everyone else had problems continue, I didn't. Recently the neighbors behind me left and their dog's ticks I guess figured they would come over to my yard and dog. I sprayed the back of my yard, PLUS THE HEDGES, and the very back of their yard too... I have no problems now!

It's a miserable issue that takes perserverence (I had to put notes on calendar!) Good wishes!