I have a white sore on the side of my tongue and it is extremely painful. i've had it for 4 days. what is it and should i worry about it? thanks!

?Aphthous ulcer?: From your brief description this could be an aphthous ulcer (canker sore). They generally resolve on their own but can be really uncomfortable. Typical treatments to numb them can be helpful. If this does not resolve relatively soon then you should have it examined.

Aphthous ulcer: Canker sores, also called aphthous ulcers, are small, shallow lesions that develop on the soft tissues in your mouth or at the base of your gums. Unlike cold sores, canker sores don't occur on the surface of your lips and aren't contagious. They can be painful, however, and can make eating and talking difficult most canker sores go away on their own in a week or two.