What Causes Red Rashes On Left Cheek?

Hi, I’m 23, 5 foot 1 and weigh 7 and half stone. I have had a red rash appear on my left cheek, it doesn’t itch but it looks like little pimples. I have also started to feel dizzy and very tired and I am finding it hard to concentrate. I do suffer a lot from tiredness but it seems to be getting worse. I have been to the doctor before who suggested more exercise which I do but this does not seem to help a great deal.