I feel like i'm 90. i get sick for weeks at a time, my hair is falling out, i'm extremely tired, etc.. this is not stress. please help.

See your MD: 18 year old gentleman with symptoms of fatigue and alopecia. You need a careful history and full physical exam and lab tests if indicated. Talk with your parents or go visit your doctor right away. Good luck.

See a doctor: If your symptoms are as you say you need to see a doctor right away

Look for help: Chronic fatigue is a condition that I believe you need to investigate with you primary physician in order to properly diagnose the cause. Hope this helps.