What Causes Menstrual Cramps During The Cycle?

HI, I am 45 and should have had my menstruation 8 days ago. I have had the menstrual cramps and other symptoms I normally have when menstruating for 8 days now. They usually only last 2 days. But there is no menstruation, no bleeding at all. Just cramps and pain, as i f I was mentruation. I made the pregnancy test yesterday and it's negative. Should I be concerned??? thanks