Do I Have Insomnia ? ? ?

Throughout highschool I have never had a regular sleeping pattern. This arose only when I started highschool. It seems like I get into bed turn off everything and stare at clock for at least 2 to 3 hours every night. In the end I usually get about 4-5 hours of sleep on weekdays, on weekends I sleep in usually to around 1-2 pm. I feel utterly exhausted before I go to sleep and can't seem to sleep though. I also have the privelage of early morning classes at 6.50 a.m. So i wake around 6 a.m. When I wake up I'm am either super tired or wide awake. But once I'm awake throughout school I am perfectly awake. But once I get home I completely crash. I really need some help here I fear this is effecting my schooling and my overall outlook on life. I mean things seem way more depressing when I'm tired, but when I'm wide awake I feel perfectly fine. So could you please try to explain to me if this is insomnia, and if so what should I do about it?