Can I be depressed? What cause's depression?

Idk what Im getting depressed of but does it cause you to be lazy, Im 17 yr old male & ive never used to be like this I would always like doing stuff with my friends, like playing basketball ans stuff, but now I just stay home Im even starting to gain weight cause I just eat now all the time its weird cause after fullness goes away I need something to eat again for my stomach to stay full is that some kind of eating disorder? & idk why Im so tired to I go to sleep at 10p.m and wake up at 9 and im still very sleepy its hard for me to wake up but it shouldn't cause that should me enough hours of sleep right?