If you had an orgasm, it causes the muscles to tense up in the body and then release. When they release and relax, some of the muscles in the body experience contractions- they rapidly tense and release, tense and release. You are prob. feeling the contractions in the uterus, which is located in your lower tummy area. But it's possible you are feeling contractions in your stomach, as well, I suppose. However, while uterine contractions during orgasm are perfectly normal, the cramping feeling or rather this painful sensation, is not common to my knowledge. I know an orgasm can produce painful contractions, and perhaps it's just because it's a really intense orgasm. However, I did a net search for painful contractions and orgasm and found this link for you: http://yourtotalhealth.ivillage.com/sex-painful-contractions-after-orgasm.htmlThat link not only lists some reasons for why these contractions may be painful for you, it also lists a small piece of advice on preventing painful contractions. Good luck!