The important thing is not to give up. You may feel as though people don't care or nobody cares for you or watches out for you but they do.
I agree with some earlier posts about finding a hobby or something to escape to. I had a friend who experienced the same feelings as you. He found solitude in listening to classical music. Yeah it may sound silly but whenever he got upset or felt depressed he would listen to some soft tunes to cheer him right up.
If you find a hobby that you really enjoy then you can always go do the hobby whenever you feel down. LOTS of people find this sort of thing in music. Music is a beauty, it's pure creativity and thousands of people listen to music to make themselves feel better about things. Why don't you try it? Explore some different genre's of music and you may find something that will make you feel much better.
If you would like us to help you if you feel up to it please tell us why you feel this way. I'm not a medical expert, I'm just a 15 year old kid but I have had those feelings before and I know plenty of people who experienced this, so please if you want to/can tell us what's making you feel this way.
Helpwise, it may be a good idea to put your trust in someone you know, if you think you are depressed it may be a good idea to get a Counsellor or a respectful adult who will listen and respect what you feel and say.
Sometimes there can be medication (anti-depressants) to make people who feel depressed feel better.