I get painful periods too, I believe its due to an Omega 3 and Omega 6 imbalance.
When I was 18-20 years old, I was an absolute health freak, and had a very strict diet of which I cut out most of the things listed next to Omega 6 below, and I didnt have any period pain whatsoever for those years. Its now back with a vengence, I believe this is due to my currently loose diet, of which I am now making adjustments to.
Omega 6 is in everything basically, sunflower oil, olive oil, bread, cakes, biscuits, chocolate bars.
Omega 3 is in fatty fish and flaxseed.
Try cutting down on Omega 6 and start taking Cod Liver Oil (which is found in the health section of most supermarkets or superdrug or boots)
I have made some changes this month, I will try to let you know how my next period is.
Let me know what you decide to do.
And I feel your pain, you are not alone.