TTC/Irregular Period

My boyfriend and I recently decided to start trying for a baby. I stopped birth control in January. My periods started out regular, but in the past few months they have been so random. I’m currently 15 days late. I took a test tonight (I’ll take another in the morning), and it was negative. Does anyone know what could be causing my periods to be so irregular all of a sudden? Is my body still adjusting after birth control? I am looking for a doctor to see, but I’m the meantime I’d love some feedback.