I'm on birth control and have missed 2 periods. pregnancy tests all say negative. what is going on?

Perimenopause: Menses occur with the normal hormonal cycling associated with ova-follicle development in the ovary, and endometrium proliferation and then shedding. As the number of available ova decline or are exhausted, the hormonal shifts are blunted or change and menses become irregular until they ultimately stop. Age of onset of menopause can vary widely. OCAs can prevent ovulation, but they don't delay age