am i depressed?

i''m a 15 year old girl, and for some reason alot of people think i''m depressed. its just people from my school that like barely know me. i go to a coed catholic school which i hate. i don''t really try to look good in school i wear a little makeup and throw my hair in a bun. i''m usually tired so i guess it makes me looked sad. i dont really talk to like everyone considering i have 600 kids in my grade. i only talk to the people i''m friends with and i try to mind my own business. when i''m out of school i''m alot more outgoing i party almost every weekend. sometimes i feel upset when i don''t have great plans for the weekend because i always want to meet new people that don''t go to my school. i''d also like to mention that my parents got divorced when i was 7, and my sister and i were forced to go on visits with my abusive father until a few years ago, when he and my sister got into a huge fight. my sister has had depression ever since then. so do i have depression, do i have a reason to be depressed, should i get help? i dont know what to do.