I have pelvic pain... I'm more than 20 days late and did a pharmacy pregnant test was negative. I don't hav fever, only that pain?

Cyst, hormone imbal. You could have an ovarian cyst that is disrupting normal hormone production that results in delayed period; could also be a hormone imbalance due to other causes that has prevented normal ovulation, and caued the mesnes to be late, and your uterus is cramping - and about to begin the menses.
See below. You should see your primary doctor or gynecologist for further evaluation.