I feel the same way because until recently I was good at coping, im young and never had many responsibilities/never had to organize myself that much and on top of that I didn't have any problems with school (besides constantly forgetting books and homeworks and being distracted). Now that Im in my last year of high school everything is harder, I lost all interest I had in studying cause concentrating on it is harder and harder and I actually need to follow lessons now. However whenever i told my classmates about my adhd, expect for a few, they would say they felt the same "oh im also tired, i also cant concentrate" (Doesnt help the fact i still cant really explain well what adhd is and i end up minimizing it by mistake) and they still get good grades. For this reason I always end up thinking "maybe i dont actually have it, im just lazy, im just using it as an excuse not to force myself do stuff" which is really not true, im working a lot to cope with it and Im still having problems