I always have leg pain when on my period. i can't function unless i take some pain killers. not as bad when on pill though. what's wrong with me?

What part of leg?: If it is the buttock or thigh, it may be referred from the back, and back pain is common with periods and pregnancy. If it is below the knee, some of the nerves passing through the pelvis might be irritated; with the link to periods & pill (hormonal changes) it is possible you may have a condition called endometriosis. Check with your gynecologist.