Poor Itchy Doggies!

My two dogs are always scratching themselves, and i dont know why. I've given them flea baths, I bathe them every other day, I've washed and re-washed their blankets, I spray the areas down where they like to hang out with this anti-flea stuff a lady at Petco recommended, I've even been burning those citronella whatever candles outside. They're on the right preventative care meds from the vet. But they still scratch all the time! I feel so bad for them. What else can I do to make them feel better??