My 15 Year Old Son, 220 Lbs, Has Just Been

My 15 year old son, 220 lbs, has just been prescribed clarithromycin 500 mg for a sinus infection. He has a nonstop gunky cough. Can he take nyquil with this medicine to try to get some rest tonight? If not, is there an over the counter cough medicine I could get from our 24 hour Walmart that might help him sleep? Thank you I"m sorry, I just saw the $15 fee. I'll ask my doctor tomorrow. Thank you for your time.