15/m low self-sesteem, paranoid...

hey, im 15 years old and im really depressed. I have a very low self-esteem and im really paranoid. I also think about alot of crazy things which really annoys me. The main thing that bothers me is I laugh for no reason all the time. I see someone that i know or something and i start laughing for no reason. Then when im playing baseball or something, i cant concentrate, cause someone will say something funny and i will concentrate on that and i will screw up. Nobody knows how really deeply depressed i am inside. I sit at home all day and lisen to angry music. I have like no friends at all...my best and only friend is my dog....how fuking pathetic is that. I just sit at home all day and be bored and mad thinking crazy thoughts that piss me off, and then when i go somewhere and see someone i know or sumtin, i get all nervous and i start laughing alot for no reason thats why no one knows how deeply depressed i am. DO I HAVE SOMEKIND OF DISEASE OR SOMETHING CAUSE I AM GOING NUTS!! SOMEONE PLEASE HELP ME

You don't have a disease. It sounds like laughing is your coping mechanism for when you are uncomfortable or nervous. That is not weird, it is actually quite normal. Everyone has their own way of coping with uncomfortable situations, and many like you laugh.
As far as your dog being you only friend. That is not pathetic. My dog is my best friend too. Yes, maybe it would help for you to socialize more. You are still young! Go out there and have fun.
Maybe you should talk to someone, professional or parents, about how you feel. Why is it that you are so angry? Why is it that you are depressed? Getting to the point of the problem may really help you.