My Dog Has Sores Under Her Lower Jaw And Around

My dog has sores under her lower jaw and around parts of her lips. Its rough and crusty. She is Yorkshire Terrier. It is causing her severe discomfort. I've tried antibiotics, antibiotic cream and Benydrl cream.
I took her to a Vet and she said just to put antibiotic cream on it. She was there getting her teeth cleaned is why I have the antibiotic medicine. I have been reading on the Internet it could be caused from allergies. I'm feeding her chicken and rice and have her off anything with wheat. I don't know what to do at this point. Please give me suggestions. I'm going to call another Vet as I'm disappointed in the one I have. What tests do I need to run or medicine can I get her some relief?