Periods so close together?

Kayla

I started my period on April 18th, and not even two weeks later started it again. They were both normal periods, normal length and everything. I’m on birth control pills so idk if that’s throwing it off? I didn’t start my period for my sugar pills in May, and I still haven’t started it again? Pregnancy tests are negative. And my periods are always on time. What do you think can cause this???