It sounds like a muscle cramp to me. Not that I'm especially expert in these matters, but I would say there's no such thing as normal - some women don't want to be touched, some want to hug, some take half an hour to get back to normal, some get paranoid(!)... no such thing as normal!
Probably ought to get your GP to check it out.
My ex-partner used to get this. Eventually she found she had slight adhesion of (if I remember right) a ovary to the body wall. The uterine muscle movements at the critical moment were pulling on the adhesion. In her case it was not too much of a problem except for the pain itself -- but perhaps in yours it could be a symptom of something more serious? Hope not...
I agree with the above post, ask ur gp to give u a check up. There are a number of differnt things that could cause the pain. It may be a natural part of your own reaction to the hormones but you should get it checked out.