Its weird with me. at first when i got my period i had pain in my stomach (for the first day), then for some time i didnt have any problems, no pain or anything when my period started. Now again past few times have been really awful, i had terrible pain, i pretty much couldnt even move myself, i was dizzy, i was shaking all over my body and i even vomited - i felt like i was going to die (i took in some painkillers before the pain started, they didnt work, as usual) . that feeling lasted about 2-3 hours and i was back normal then like nothing had happend, felt great.
for some time i had my period after every 2 weeks. i couldnt understand why :S (i havent been on birthcontrol pills or anything like that). at moment its not that regular either, but at least its once in month.
some friends of mine suggest me to see a doctor about it just in case.