Why has my menstral cycle changed from having a period every month, to only gettin it every other month for the past yr. i am 24 cycle is about 85 day?

Many reasons: You should start a work-up with your gynecologist. Poor ovulation(s), and thyroid or other hormone imbalances are some of the possibilities.

Schedule a visit: The next step is to schedule a visit with an ob/gyn to evaluate the causes of irregular periods. Irregular periods occur when you are not ovulating. Ask to be tested for pcos.