Please help - adult acne

My son is 25 yrs old. He has never had acne or even many pimples until now.  Now he gets reoccurring pimples only on his forehead.His forehead is the only part of his face that is constantly oily.  He has tried all the different popular treatments He's tried home remedy treatments.  He completely changed his diet and is very strict about not eating anything that causes another breakout.  Each time one  goes away - there's another 2 or 3 erupting. He does not over wash his face.  He moisturizes but careful not to use much.  His hair is short and not on his forehead.  He made a trip to a dermatologist that recommended Cerve and other treatments) - tried that didn't work.  He is extremely depressed.  He will not go out of the house because of his forehead.  He's so self conscious about it and EVERYTHING he has done is not working.  He is  desperate to get his  forehead cleared.  It has really caused him to have low self esteem and I am extremely worried about him.  Please help!