why do i have such bad mood swings?!

Best Answer - Chosen by Voters

I used to get really bad mood swings when I was on the pill, this might not apply to you but now I no longer take any hormone contraception and I find I am a much happier person! Also could be your sleep (getting enough too much) or your diet. Have a little think about your lifestyle you maybe able to cheer your self up!

To an extent, such things are due to hormones when we're young. If these mood swings are very extreme, and/or they continue into your twenties, it probably indicates a mood disorder, usually Bi-Polar disorder. I recommend seeing a therapist.