Skin rash and scratching

Question
I have a 2 year old Pomeranian/Yorkie that the vet now says is allergic to fleas. I have bathed her in Zodiac Protein conditioning Shampoo that kills fleas on contact, Natural Oatmeal Shampoo and Hartz Hydrocortisone Shampoo but, she is still scratching and biting and it's getting worse. Could there be something I'm missing? Should she get a steroid shot? (she's had 3/4 throughout this year and it did help her) or, is the colder weather and heater drying her out more?
She has little red spots on her belly, some brown spots on her back which I've checked to see if they are flea eggs and they are not and, I think her hair is getting thinner. I have two cats who get flea sprayed regularly and don't scratch or bite. Please help! Thank you, Lisa

Answer
Yes cortisone shots followed by tablets will help relieve the itching.  I always recommend using a topical insecticide like Frontline to controland prevent flea allergies.  Once the fleas bite the dog, they can cause itching for 30-45 days, so shampooing after the fact will not help the allergies,butit will kill the existing fleas.