Mood swings?

Lately, i've been having these mood swings over the last girl i liked. I'm not sure why, sumtimes, i'll be in a really good mood where I don't even pay attention to her, other times i'll be all depressed about everything and others, i'll be so freakin full of myself, I'll be like, i don't need that bleach blonde tramp to make me happy. and they happen at random times of the day. Also, one side of me will be like, screw tht b*tch and let's go get w/ sum other chick. and the other, will still care about her and wants to still like her. I don't know why this is happening, plz sumbody explain why this is happening or how to get over it...