The type of the lesions which you have described here that it started with white spots
and blisters and afterwards they turn red it looks like that these are aphthous ulcers
. This is a very common disease which occur in the mouth. It starts when there is stress
or some stomach problem etc. Generally it heals on its own but when there is problem while taking food you can apply an ointment on the spots (ulcer) . The name of the ointment is mucopain.