Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern... As per your complain and presentation of symptoms fever and mouth ulcers are due to allergic reaction to the antibiotics that have been given to you by the dermatologist.. Due to allergic reaction there are ulcers in mouth and fever is also a process by which the body s immunity tries to ward off the allergen by rising the body temperature.. You should immediately stop the intake of all kinds of antibiotics and consult your dermatologist.. He can change the medicines and also advise you to take anti allergic medications like Allegra [Fexofenadine] or benadryl[diphenhydramine] so that the allergic symptoms gets improved.. You can apply numbing gel containing Lignocaine over the ulcers for pain relief.. Do warm saline gargles.. Gargle with 1:1 solution of benadryl and milk of magnesia can help.. For pain you can also take Ibuprofen.. Suck on ice pops and do cold water rinses as it will reduce inflammation and pain.. Avoid hot spicy and citrus foods.. For fever reduction you can take Paracetamol.. Take sufficient rest.. Get an allergic testing done and after that only take antibiotics which are not found allergic.. me directly by visiting my profile and clicking on ask me a question.. For any further queries you can consult Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora..