What Causes Spots On The Inside Of Cheek In The Mouth?

hi, im 20, i am about 5 foot 7' . my medical history emm.. i have a bit of eczema.. nothing real major.my question is i got an irregular spots on my inside cheek of my mouth and it if i keep touching them with my tongue i get tasteless tongue. but i had these spots like 4 mouth ago but they disappeared after around 2 and half mouth and now they appeared again. i went to the dentist he said if they disappear and appear some where else they are alright. but i dont get why they keep coming back?