25 years old don't know how to look for help

I'm 25 years old I've never been diagnosed 
I know I need help, I've always known I might have depression 
I've used to have some suicidal tendencies in the past ( I used to cut , it's been 3 -4years since I've stopped) 
Everyday I feel horrible. I feel like a mess, I feel like I'm not worth it;some days I feel so sad for no reason or I get mad really easily for no reason . 
I feel like I'm tired of living like this . I want this to be over. I'm going to see a doctor 
But I'm scared they won't believe me or think I'm just tired or something else 
But I know it's not that I'm just tired
I know I need help