Well, could be some sort of hormonal changes are causing you to have severe gas, which some women do have bad gas during their cycle, which would explain the once a month thing. And even if it's not directly connected to the cycle, we have changes going on all thru the month. I had that kind of pain when I was in my teens after eating a big meal, it was so bad that all I could do is just lay there in terrible pain in my tummy and side for hours until it finally went away. A relative told me she had it when she was a girl, told me to take an alka seltzer, and when I did, it went away. I don't know if that's it, but give alka seltzer a shot, it dissipates the gas, and see if it helps. If it turns out it's not gas, you could have a gyno doc do some labwork, to see if your hormones are way off the chart, especially since this a monthly thing.
^forgot to mention- 23 year old female. Also completely healthy and symptom free the other 29 days of the month.