I keep getting mouth sores. they start out swollen + painful but swelling goes down in a few hours, and sore disappears within 2-3 days. like canker sores but too brief to be those ... what are these?

Best 2 see a Dr.: Or dentist or oral surgeon when you have the lesions so they can be seen by the provider. If not possible get a clear (not fuzzy, out of focus) picture to show. Some times mouth sores can be from viral infections, sometimes extra b complex vitamins help.

Sores in mouth: If recurrent lesion is herpes labialis your immune system is good so it last less time.

Canker sores: These are compatible with canker sores although I do agree that the 2-day duration is shorter than average.

Mouth sores: Any recurring lesion should be examined clinically. They could a result of a viral infection, an allergy, or some other type of infection. Have them examined by your dentist.