What Causes Cramping & Bleeding During Menstruation?

i've had an iud since june 2008. i may spot every 4-5 months. I had intercourse 2 days ago and after i was in so much pain that i couldnt stand up straight. My husband had to take me to the bathroom. No bleeding. The next day, the cramping is still there but still no bleeding. Today, i coughed and blood started coming down my thigh. i washed up and put on a pad. I have only filled one since 1pm but now i have clots. What do i need to look for for the next few days?