18 years old, no cancer or diseases.

Turning 19 in one week, ever since i was 14 my mind has been elsewhere, i cant concentrate, feel emotion, and im tired 100% of the time, really tired! I started smoking marijuana and tobbaco when i was 16, but please remember these things started happening years before, no doctor has ever been able to tell me whats wrong with me, i quit smoking altogether for 30 days and nothing lifted, my stress level is through the roof and i feel like im dying inside, i want to start living my life instead of being a zombie, can anyone relate? Does anyone have any idea whats wrong with me? My eye sight is blurry and my nerves are messed up, my fingers will twitch, so will my left eye, anything? Starting to lose it.