There are many causes for mouth ulcers, including the ones you mentioned, in addition too, a bacterial, fungal or viral infection, neutropenic, anemia ulcers, other medical conditions, rubbing on a tooth, biting tongue while sleeping, rough or sharp foods, spices, medications, smoking, drinking alcohol. Glad you went to the doctor, any sore or anything unusual, not going away in two weeks should be checked out like you did. I would also suggest changing your toothbrush, as not to reinfect yourself if it is an infection. Most times it's something else other than cancer. Maybe also have a blood work up to see if anything is out of range or shows deficiency. Good luck with the biopsy.