Depression. Of what i should do next.

I don't know what depression exactly is like because i have never been diagnosis moreover i have never been to a psychiatrist or psychologist but i think i might be depressed but i don't want to assume and emphasize on that. most of the times i feel weird idk if we can call iy sadness but it's more like emptiness and i have been dependant on stuff like nicotine and alcohol from a young age and even that doesn't work properly anymore. even when everything around me is alright i can't seem to feel alright most of the time and maybe i feel a little lonely but in reality i do have few good friends who look out for me and a boyfriend and to be honest my parents aren't that bad. i pretty much don't know what to do and i feel like getting a diagnosis might give me some closure and idea of what i should do next.