constant dry cough and coughing up dark brown stuff?

so ive been having a dry cough for more than 5 months now & im always clearing my throat. i also have recently started to cough up dark brown mucous and dark green. mostly in the morning, but i also get it through out the day on occasion. im pretty fatigued over things that i shouldnt be, my throat is sore off & on, and overall feel like something is wrong. i recenelty had an upper endoscopy done and found nothing, and ruled out gerd/reflux. i was put on prilosec & nexium just to be sure for 2 weeks, and im going back to the ENT on wednesday. anybody have any idea on what this could be? im literally only 16 and no idea why im feeling this way or whats going on. idk what to do.

ive tried this stuff;

nexium, prilosec, prevacid.

allergy pills.

ibuprofen.

and a lot more.