Hi dear , Well this is very common problem in teens .There are some factors that trigger the formation of pimples . The most common are oily skin , stress , sun exposure and hormonal changes . As per your query your skin is start getting darker , it seems to me you must be using some ointment or cream containing steroid , hydroquinone or teritenoin . Thses ingredients has long term side effects , they make skin darker and red in long term . I would suggest you to wash your face twice a day with facewash containing benzoyl peroxide , after washing face apply cream containing azelaic acid which safe for use and consult dermatologist again and discuss your condition . Doctor may prescribe antibiotics like clindamycin or minocyclin. Hope your concern has been resolved. Get Well Soon. Best Wishes, Dr. Harry maheshwari