hello my dear,
as laurendhh says, please see a doctor. and it sounds exactly like me as well. that's when i started or maybe actually recognized my mood swings.
growing up with it was a bit confusing for me. first i dint know it was actually a condition and i was having it.
it was a struggle for me, just like you. i can so relate to you. i still do have anxiety attacks (that's what i call it), unnatural happiness, and sometime my laughter gets uncontrollable, and the other side is sadness, crying attacks, and a lot more.
one thing my dear, i need you to do is, never let it over take you. its a very difficult thing to do. how ever low you feel, or you fell you are going down, then move, do something fun, have a chocolate, or ice cream, listen to some energetic music, sing, run anything that would get your brain pumping. on the other side, be careful of the highs... stay back, make sure your actions and words are controlled (i hate it, its got me into so much trouble.). i know its extremely difficult, but just don't let it eat you up. and finally... talk... write and speak to your self in front of the mirror, its a relieving thing to be letting it out looking into your own eyes.
I'm really happy that you are not thinking about suicide. remember dear, there are so many people like you, and there will be immense support for you. and finally please see a doctor. it really helps. you will know where you stand. and since you are young, it will be great to start early on, on battling things that make you feel high and low...
love you, and hope you have a wonderful life...
all the best!