As per the details provided by you it looks like a mucocele . The extra teeth which is growing might be hurting your lips due to which mouth ulcer or mucocele has formed. Mucocele  if small usually heals by itself ,once the sharp tooth edges has been smoothened or If extra tooth then it should be removed.

Ulcers are due to trauma but is mostly painful. But the description you are telling seems to be like a mucocele. In an oral mucocele, saliva is trapped and appears like a blister in the mouth but when the blister ruptures, the ulcer is formed which is painless. It could be due to frequent trauma in the area of your salivary glands, like lips, floor of mouth, corner of mouth etc. And you were saying about extra teeth growing in corner of your mouth, kindly share your photos of the tooth, for diagnosis. It could be a supernumerary tooth, but need to investigate further.

It could be a mucocele if it’s on the lip. Consult a dentist for proper treatment