My menstrual cycle has came on time every 28 days since the onset. This year, it has been coming every 23 days instead. Why? Aa female, 34, no kids

Hormones. Your pituitary makes precursor hormones that tell your ovary when and how much estrogen and Progesterone to make, which determines the length of your cycle. Cycles do change over time. So long as no pituitary or thyroid problem, then change in cycle is due solely to changes in natural hormone production. Birth control pills can help regulate to 28 days, but unnecessary if that's only concern.