Hormones are the biggest culprit when it comes to pimples on the cheeks or forehead. If you are just entering adolescence or are a young adult, you are predisposed. Oily skin, which can be triggered by hormones, can also be responsible. And, genetics often plays a role. You can try using cleansing products that contain salicylic acid or other acne treatments. If they don't clear up talk to your doctor about stronger ointments or cleansers.
Whatever you do, don't scratch or pick at them. Bacteria underneath your fingernails will enter the pores of your skin, worsening the symptoms. The best thing to do is keep your face clean and free of excess oils from your hands. Reducing stress can also help maintain a smooth complexion.