What Causes Pain Under Rib Cage During Periods?

For the past 4 months, on the 1st or 2nd day of my period, I get very serve sharp pains under my right rib cage area. It's so bad I can not breather or move. The pain last non-stop for almost 2-3 hours. After that it stops, it only happens those couple of hours and doesnt happen again until my next cycle. I have never had cramping or pains during my period, now at 27 it's those 2-3 hrs and the pain is worse than child birth. Im 5'4 and about 185lbs, no other history of problems or complicatiosn