Antibiotics and not eating

[Dogmomforever]

We have a 11 year old pit bull who developed a lump under her jaw about 3 months ago.  She was treated for an infected tooth With 2 rounds of meds and also a dental cleaning to make sure the tooth did not need to be pulled. We thought we were good.  But it returned 2 weeks ago. This time the vet took a sample, which came back as just an infection, and he put her on a very strong antibiotic that he has very good results with and said she needs to stay on it for 3 weeks. She is on her second week. She is drinking water, but has not eaten anything significant for about 4 days. We have tried her wet food, chicken and rice, scrambled eggs, McDonalds hamburgers and fries, she won't touch anything now. We have discussed this with the vet and he doesn't seem too concerned yet. Does anyone have any suggestions on what else we might try? We are getting desperate and willing to do anything for her.