Im 2 months Late **PLEASEE HELPP*?

ok im 15 and ever since i've started having my period its been irregular. Im not a Virgin, but i took a Pregnancy Test about a month ago and It was Negative. I've thought about birth control, but i cant start it until my period starts sooo my Question iss What the Heck Is Going On With My Body !??!?! Is Birth Control a Good Idea.???