Do I need physiological help?

I keep thinking about kissing and love etc. and I am single. It takes over my thoughts most hours of the day and it bombards my dreams. I used to self harm but I haven't since november but I keep getting frequent urges to. I sometimes feel like committing suicide because I feel the world would be better without me and I frequently feel like crying. Im very pessimistic and when my friends try to give me advice I keep saying that everything won't be ok. I don't know whether Im depressed, need help or its just teenage hood.