First of all you need to be assessed about how many ulcers ,where all you have,and how often you get,is it occurring in the same area multiple times. And a very detailed history would arrive at a proper diagnosis.First you better visit your nearest dentist preferably an oral medicine specialist and get treated.Till the n use mucopain gel on the ulcer.

There are multiple causes for oral ulcers. The exact cause in your case can only be determined after a complete clinical examination and a detailed history. Till that time, anaesthetic ointments like dologel CT can provide temporary symptomatic relief. Regards.