My period is 20 days late, but i've had 5 negative pregnancy tests. what could be wrong?

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, but the median is about your age.