what happens if you go to the doctor for depression?

ok so for like the last 7 months I've been feeling really sad all the time and I cry for no reason. its usually way worse at night and it keeps getting worse I think about how badly I want to kill myself. and I haven't done this for so long and then the other day I cut myself. Now my boyfriend made me promise I would see a doctor about it. its just a regular doctor that i'm going to go to and I don't know what I should tell him. I really don't want to go. and also is it ok to go to like the same doctor I always go to. I don't know how much I should tell the doctor and what he will do when I tell him.