Depression

I haven't been to see a professional about it and I don't want to wrongly diagnose myself but I've been feeling severely sad and under the weather for no apparent cause, I constantly put myself down because of things I do, I've selfharmed before- which I seriously regret because my family found out and it was embarrassing, but I really felt like I deserved the pain I was giving myself. I'm getting feelings/urges to self harm again, and am having reoccurring thoughts about suicide. I know that sounds pretty extreme but I'm not sure because I've been feeling like this for years, I want to reach out to you people who might know what I should do and whether I should go and see a professional about it or find a way to sort it myself.