I stopped using Frontline. It wasn't working anymore, apparently the critters are becoming resistant to it. Figures
I would also recommend doing a spray on your carpet and bedding, my dogs get itchy with a couple of flea bites.
You may need to do an elimination diet...some dogs are super sensitive to certain foods. My sis had a dog that could have no chicken, turkey or eggs, not even a tiny bit or he would have the same symptoms. It took a lot of time to figure it out, he was on a few allergy meds and they didn't work well until those foods were taken out of his diet.
Hope you figure it out!