Diagnosis?

I feel like even though I describe it my parent's won't understand that I might have depression unless I get a diagnosis. What type of doctor diagnoses a mental illness? Also, I'm not sure if I have it or if I'm diagnosable. I looked online and I have almost all of the symptoms but I also recently had a somewhat traumatic event. The depression could come from that meaning I don't have the disorder. It's hard to tell because I have gone through periods of depression like this a lot through my life. Any insight would be helpful even though I know no one can diagnose me over the internet.