The problem with fleas is, you have to treat the whole life cycle. The eggs, the larvae, and the adult fleas. This takes multiple treatments over a period of time. There is a lot of information available online, just do a search for fleas and you will find tons of detailed information. You shouldn't have to buy any expensive treatments, but it does take a long time. The eggs can survive unhatched for a couple months I think (I forget exactly how long) so if you don't get rid of them, then just when you think the fleas are gone, bam, a new generation hatches. One thing that helps tremendously: after each treatment, vacuum several times a day for about a week. It's a lot of work, but it will get rid of them. Eventually.