I had this same thing recently. I got it from the super cold weather where I'm at. I did it on accident and then it got yellow crusts on them and I was freaking out. It really sucked.
Anyways, I just let them be as much as I could and tried not to open my mouth too wide but it wasn't helping much. Honestly, I was already starting to incorporate a healthier diet very slowly. Now I'm doing pretty good with diet and it just healed by itself after about a week of eating very healthy. They still bother me every once in a while but there pretty much good now.