Hi,
There could be numerous reasons why this could be happening, such as: stress, medications, side effects from birth control, hormone imbalance, miscalculation, and so on... If this happens continuously, you should start keeping track of your menstrual cycle and consider speaking with your doctor about this soon, just to rule out anything serious.
I have been tracking... I'm not on any meds including birth control, I feel like they just wanna cut me open