My Pem puppy has fleas. The fleas spread to one of my other dogs. We gave them bathes with dog shampoo meant for killing fleas. They still had fleas after that. WE brushed my corgi with a flea comb, but not the other becauseshe has lots of matts in her coat. I gave them bathes again with the anti-flea shampoo. They still scratch and bite like they have fleas (which they probaby do). How should I get rid of the fleas?