Contraction like pain in pelvic area...

I have been experiencing some pretty severe contraction like pain in my lower pelvic/rectal area.  The pain hits me like a wave and only lasts for about 5-10 seconds, but it stops me in my tracks and nearly doubles me over it is so severe.  I am currently on my period and it has only happened twice today, but I know I've had this pain in the past and just dismissed it.  I can't remember if I was on my period during those earlier experiences.  I see a gynecologist regularly and have never been diagnosed with anything other than cysts on my ovaries, but that was many years ago.  Any ideas on what this could be?

[moary]

you can take a pain killer to ease your pain and make an appointment to see a doctor for a check up