I think you answered your own question by the facts you presented.
You are 15 and yet you have enough stress in your life to be getting canker sores and know, much less care what "foycde spots" are. You seem to focusing heavily on what might be wrong with you. What's up?
Why are you stressing yourself out so much?
Note: I'm not a doctor, but you might want to talk to your parents and Doctor, Nutritionist, Natural Healthcare Professional about Zinc and B12 supplements for the sores.