What is wrong with me?

I think there's something wrong with me, sometimes I feel so depressed, I just feel like sleeping all the time, and other times I feel like excersising, and I become really outgoing, friendly, sometimes aggresive and really ual. When I'm in one of the latter moods I spend whole nights having , drinking and smoking with my friends, when I'm in the first mood I described I just go home and go to bed as soon as I come home from school and feel like doing nothing. I'm very intelligent, intellectually for my age but I find it so hard to focus sometimes. Im a 14 year old boy living in the UK.