The lesion appeared on the picture is different from your descriptions. The lesions appear to be erythematous, flat , ulcerated, well demarcated . Clinical differential diagnoses include , but not limited to,traumatic ulcer, vesiculobulous lesion,hypersensitivy. If the lesion does'nt resolve within 2 weeks, seeing an oral pathologist is advised.
The lesion may be an abscess or a hematoma. Seeing a dentist is advised.