I get depressed very easily?

I had a severe case of depression before when I was 12-13 ish that Ive kept to myself and overcame myself without telling anyone. It was really hard to get over, and even then, I don't think it's gone. I was okay a year or so, but slowly the depression seemed to sink back in. I'm 15 now. I'm a tough cookie, independant and dominant yet somehow I get super depressed over the smallest things. An I sensitive or something?like I go on facebook and read a status or two, hang out with my friends or just eat something that makes me depressed. I cry myself to sleep everynight as well, and I have harsh mood swings. I'm happy, then angry, then sad, or any other order of those emotions. I don't get it. Last year was so fun, so bright and happy for me. Now it's like suicide season. I can't go to a doctor. My parents don't support me, in fact they make fun of me, assuming I do it for attention or some stupid crap like I don't deserve to be sad. Can anyone tell me what the hell is wrong with me?