Hi.. Thanks for the query.. Most common cause for mouth ulcers along with fever is viral infection.So in case if it is viral infection antibiotics like Levofloxacin will not help as they are capable of treating bacterial infection.. So my suggestion is to consult your doctor and get her evaluated and he can do a mouth swab culture and a blood test to rule out for the exact nature of fever. In case of viral infection anti viral medication like Acyclovir will be advised orally as well as for topical application. Along with it Acetaminophen should be given to reduce fever. Along with it gargling with Lidocaine mouthwash will help in relieving pain due to mouth sores. Doing salt water rinses will also sooth the mouth. Do cool compresses over the sores outside the mouth and apply Lidocaine gel.. Take soft diet and bland foods and drink plenty of water.. Note: In case if viral infection is diagnosed it will be better to avoid close contact or use common towels etc as it is a communicable infection, so it is better to be cautious to avoid transmission of infection. Hope this helps.. Regards.