i've had these problems since i first got my periods at about 15yrs old. i've told numerous gp's and no-ones ever told me what it could be or explored it further. i did notice an improvement when i went on the pill, and then when i went off it and fell pregnant i noticed it disappeared.
however since i've had some loss (like a period) after the birth of my child i've noticed it back again. i'm glad i'm not the only one with this. i know for me it can get pretty painful some months and others it's barely noticable.