Sometimes i get to feeling really crappy and i think about ways i could kill myself?

I get to feeling crappy and i'll think of ways i could kill myself. Now i never go through with it but still, it concerns me. And yesterday i got to feeling that way again about halfway through my school day and I began to cry on my way home when i was driving. Its like i had no control over it. But then when i got home i cried some more and then its like i was just fine. And its happening again right now. I just don't understand it. And by the way i'm a 16 old guy. I don't like admitting i cry and I very seldom do. The only thing that concerns me is that my uncle on my dads side has some sort of mood disorder and as a result he attempted suicide last year. Also my mom was diagnosed with bipolar about 3 years ago. Could some1 please help me. By the way i normally don't tell anyone about this but two years ago i used to babysit for my parents and didn't have a life and i felt overwhelmed and I took 9 clonadine pills ( i used to take them for "trets" but i was misdiognosed) after that i took lexapro for about 3 months and then got taken off of it cuz my dad didn't think i needed them. But I still get the thoughts sometimes when i get really crappy feeling but i just haven't gone through with it. could some1 please help me understand what going on with me. I don't have anybody else to talk to:(