What Causes Delay In Menstruation Other Than Pregnancy?

I just started taking birth control pills back in feburary, and i had my period in march and in feburary...but in april i didn't. It is now May 3rd and I have no idea what to do. I skipped a couple times in april but always doubled it up like the instructions said to. I am totally lost right now, should i be worried? Was/am I not suppose to have a period now? I took an at home pregnancy test, but those aren't always accurate? What do i do?