Here lately i have been having pain after my husband ejaculates inside me, and my stomach gets rock hard. it has never happen before?

Inflamed cervix: It is unlikely that the semen itself is causing the symptoms. At the time of male orgasm there is often a thrust forward perhaps irritating the cervix. Cervical irritation is most likely the cause of your symptoms. As a result the uterus, as an extension of the cervix, can spasm causing the pelvic discomfort. Please see your primary care or gyne to assess for cervical inflammation or infection.