Hi. When you say you have described this to two doctors, were they GPs or gynecologists? Did either one of them take a complete history and do a pelvic exam or prescribe blood tests? Do you have children, or are you trying to conceive, or have you had a history of problems with conception?
Are you on birth control or other medication?
Otherwise what are your periods like? Pain free, and you hardly notice them, or is this just so extreme that it makes painful periods seem simple in comparison? Do you have cramping or bloating at other times in your cycle?
I'm sorry if I've asked you a lot of questions, but usually when something such as you have described occurs, there are often a number of other things going on that need to be taken into account, and often one doesn't think of them, yet they can be important when trying to diagnose what is causing the problem.
I can't diagnose it, and in fact no-one here can, but if you start to consider other aspects of your health, your cycle, and what you are facing, you might find there is more to this than just what happens on the first day of your period. If you can then track a variety of symptoms and have a list of possible causes in hand when you next see your doctor, then perhaps you can nudge him or her to doing more than just saying they have never heard of what you have described to us here.
Best of luck, as this is one of those things that can take some time to sort out, and often requires a great deal of input on the part of the patient - you, in this case.
KarlaCommunity Moderator, iVillage.com