I hd a lesion like an ulcer on the left backside of mouth. that one has gone down in 2 wks but another has come up on the left side. bth wr on gums .

Ulcer?: Could be from infected teeth, gums, systemic infection, reaction to meds, or one of hundreds of other oral lesions. See your Dentist for differential diagnosis and treatment.

Oral Lesion: Good Day; If I had an ulcer reoccurring in my mouth for the past few weeks- why not consider visiting the dentist! A perfect time to consider a visit! A colleague could recommend one or possibly your local hospital! Young people like to find practitioners on the internet! How about a local Health Tap DDS! Take care

RAU: Recurrent aphthous ulcers ? A distinct possibility. If you would like to know for sure, you'll need to visit your dentist during an outbreak for an exam. https://en.wikipedia.org/wiki/Aphthous_stomatitis