Please note that this type of ulcers are called reccucent apthous ulcers,  which means they re occur...  There could be triggering factors also like sharp tooth which will need to be taken care of professionally.  It is ideal to not consume any hot or spicy food which will aggrevate the ulcer. Medicated ointment will give relief but you have to visit your nearest dentist to find the root cause of the ulcer.