Period Problems

Okay, so I haven't been on my period for 3-ish months now, and am so worried that it will just pop in whenever. And I got my first in January, and it was normal for February then just stopped and now it's May and it still isn't here, any advice. Please, because it's kinda freaking me out. and I know for sure I'm ABSOLUTLY NOT pregnant. seriously. I'm not even 16 yet.