If your referring to blue balls, there are plenty of articles that discuss the topic.

Pelvic congestion is a condition of temporary uncomfortable and sometimes painful condition of both men and women, usually caused by prolonged sexual arousal.

Women can also experience discomfort due to unrelieved vasocongestion as their pelvic area also become engorged with blood during sexual arousal. They can experience pelvic heaviness and aching if they do not reach orgasm.
I agree with EB though, see a doctor to make sure there isn't anything seriously wrong.