Is this depression or just something harmless?

Well I've been feeling depressed lately.It's starting to come back stronger and stronger.I usually feel sad for a while and then get back to be a normal person that is content and focused but when I feel sad I become distracted;I can't think of anything else but the problems in my life.I've been wanting to hang myself and I also sometimes wish someone could just come and shoot me in the head to put me out of my miserable life.I also feel like I'm the ugliest person in the world.I know it's strange for a guy to say this but it is true,sometimes us guys feel like we look like turd in the grass.I also feel like I don't really matter in life.I just feel like I'm not important and if I were to die,nobody would care or notice but I have this feeling also that if I do die,maybe someone will care.I don't smile or talk much.Most people think I'm a weirdo or a freak.I don't really take care of myself because I lack motivation.I don't see the point of fixing myself up for the world.I'm seventeen years old and I'm going to graduate from high school in a month.I also feel like I don't have a purpose in life.I keep telling myself that I do but...I don't feel I do.I feel like I'm just lying to myself.I also had a pretty messed up middle school and high school life.I'm too scared to make friends because I'm scare they'll judge me badly and I'm still scarred from an experience like that.I usually keep quiet and don't talk much.I don't do much eye contact either.So...is this depression or just phase in life?I need to know because I'm thinking of seeing a doctor about this.Thank you for answers everyone.