All dental professionals are taught to indentify oral lesions. Anyone from general dentists to oal pathologist or orthodontists. We all have taken oral pathology classes. I am very saddened that some of your providers failed to diagnose in a timely manner. Oral exam is easy to do, even you can do this at home. Look on both sides of your toungue. Check for any areas of whitish patch. Look at the bottom of the toungue as well as floor of the mouth for similiar lesions. Look on both sides of the cheek. Say Ah and look at your tonsils and your throat. If in doubt, go to a dentist for a biopsy. Every single lesion in the mouth must have a diagnosis whether it is an ulcer due to trauma (say from a rough edge of a tooth) or a harmless blocked minor salivary gland. As I mentioned before, it a diagnosis cannot be rendered, see someone else who can. DP