I have redness in my mouth on my cheek and flat white areas..what is it?

Yeast or....: This could be a simple yeast infection, a common disorder called lichen planus, or something much more serious. Have a check up immediately. You may only need a prescription mouth rinse, but it should be looked at.

Exam needed: Your question cannot be answered here,, it needs to be looked at to get a diagnosis. See a dentist ASAP and get it checked. There are a number of things that can cause this.

See your dentist: for evaluation and oral pathology screening. See your dentist for mouth lesions (red or white) that persist longer than two weeks.

See dentist: Hard to say. You should see a dentist to have the areas evaluated and possibly even swabbed, smeared and tested for what the cause may be.