fleas!

Help, I have been to the vet this week because Molly (my 1 1/2 year cockapoo ) has been itching her head a lot, i thought there was something wrong with her ears, However the vet found a number of live fleas on her. I have been dilgently applying 'frontline' ever since i got her every 2 months (as directed by vet). Its obviously not working I applied an extra dose when i got back from the vet on the vets instruction however 3 days later theres still live fleas on her. You apply it directly to the skin at the back of her neck but as her hairs quite absorbant it is quite hard to just get it on the skin as the hair soaks it up and i wonder if thats the problem. Has anyone else had flea problems and what products do you use. I'm having to spend a fortune on a spray to deflea the whole house!!