Why i Cant sleep? (help?)?

im 15. ever since i was 4, ive had a problem sleeping. i have to up till almost 1 am to even have a chance at sleeping. some nights i can just lie on my bed staring at the ceiling for hours. I don't know if this is some sort of problem or not. also, the only reason i usually get to sleep is i have to be doing something either physically or mentally exhausting to get myself to go to sleep. i haven't had a full eight hours of sleep in years. my plan is sually stay up all night one night so i can try to sleep for 8 hours the next night but that doesnt work either Help??