Em
Magic's spot on.
I had this a few weeks ago and am still having the odd ovarian twinge. Your baby is dependent on your ovaries at the moment and will be for awhile yet until the placenta grows and takes over properly at about 10 weeks. If you have an ultrasound at 6-7weeks ask them to show you your ovaries. I could see my corpus luteum on my left ovary really clearly. It looked like a great big crater. When I saw it - I thought - no bloody wonder I can feel that ovary!

The other cramping you get is in the uterus as it starts to stretch to accomodate your baby.

ETA - the corpus luteum in the remains of the follicle of the egg that got fertilized. If you think of the egg in its follicle - when it bursts it leaves a tempoary crater on the ovary. If the egg fertilizes there is a feedback loop in the hormones which somehow tell the ovary to keep all the AF inducing hormones stopped and to start producing all the preganancy hormones instead. If the egg isn't fertilised the ovary heals quickly and the normal menstrual hormones kick in instead. Look it up in wikipedia - there's a good explanation and diagram there. HTH.