It's hard to tell from the pics, but to me it looks like scale rot, but I'm thinking it may be caused by a mouth infection since the sores are in the same place, opposite of each other, and if I'm not mistaken, the "expansion slit" is also looking abnormal. Have you checked inside the mouth yet? I would suggest a vet trip to have it checked out, because you will probably need some antibiotics to clear it up...