Hi there ~
can be adding to your anxiety
and your decrease in appetite, all leading to your being underweight
. I understand that being on a new modeling contract can be stressful, however dealing with and coping with stress is how one gets to the top of where they want to be. The ulcer does seem benign (not harmful) and could have been caused by teeth whitening strips. However, I would suggest that you wait for a couple more days on the ulcer-like lesion as they usually tend to disappear. Taking multivitamins is useful.
Consulting a doctor, even if none of the above work may be the way to go. I hope it helps though. Take care.