I don't know why new quitters get the sores and such in their mouths. But I do know it's common. My jaw was sore off and on for many of my first 100 days quit. It's almost certainly nothing to worry about, but definitely get it checked out to put your mind at ease.
To get the most out of this site, and some great support, get active with the March '17 group, and post roll. Posting roll is the backbone of the site.
Oh, and quitting on your own for 2 1/2 weeks is badass.