What Causes Severe Gas Problem During Menstrual Cycles?

it happens only sometimes. i THINK its my sciatic nerve, as it inflames that and all other nerves around that area, and even the simplest rolling over motions or moving at all causes pain like i've never felt in my life. But at the same time, it feels like i have severe gas or menstrual cramps. It uh...happens after intercourse, around the time when i'm due for my menstrual cycle. Are these things obviously related, or do i have a bad problem?