I think that this is the cause, yes. I have spastic cerebral palsy, and I have found that sex makes my muscles very very sore, stiff and crampy.
The best way I have found is for lots and lots of foreplay to occur. As women, the more foreplay we get, the wetter we get down there. This preps our body, our minds, and usually will bring you to the point of really wanting to be entered by your partner. It also helps to release the chemicals so that sex isn't as painful during.
It also helps to try and remain as relaxed as possible. Talk to your body. The more relaxed you can remain, the easier it will be. The next day is usually the worst. I've found stretching and anti-immflamatories work well to make the body pain and stiffness tolerable.