It sounds like maybe you're trying to find yourself...you have a lot of questions, a lot of worries and thoughts about your life and where you're at in it, but you don't know exactly how to deal with it. You could be clinically depressed, but I wouldn't jump to that conclusion right away. First, focus on your feelings and try to straighten them out. If you are constantly feeling worthless, sad, and even suicidal then it could be more serious -- something you'd have to take further steps for, like seeing a doctor. But anyway, perhaps you should journal. Maybe it'd be easier to sort out your thoughts and identify your feelings if you wrote everything down. That's helped me so much in life. It can really put things in a different perspective! When I have been depressed in the past and forced myself to write about it, I always come out of it feeling better about things.
Another thing you could do is try to focus on the positive things on your life so that you're not always worrying. Each day, maybe write down 3 or 5 things that you're grateful for in your life. You could say that you're grateful for your parents, friends, a certain talent you have, or smaller things -- the sandwich you had for lunch, the beautiful flowers outside, your favorite fragrance.
Focusing on the smaller joys of life -- the taste of ice cream or the sound of your favorite song -- can really bring you back to reality. Living in the present and realizing what you have right now and how lucky you are to even be alive and healthy is so crucial to well-being, I believe.
Another thing I would suggest is focusing on some sort of hobby. Perhaps you should start reading more. The library is always a haven for me! (Plus, it's free.) Knit, ride a bike, write, garden, play basketball -- something, anything, that will healthily distract you and give you something to draw pleasure from.
And don't ever neglect exercise. Exercise, to me, is not only crucial to your health but it can be like a drug. Your brain releases endorphins when you exercise, which make you feel wonderful and happy. Even just taking a brief jog or long walk, riding a bike for a mile, or swimming for half an hour can do wonders for your mind and body.
Good luck with everything and I hope that you sort things out. It'll come with time. :)
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"In a world we need to share;
it's not enough to stand and stare." --Pink Floyd