What does it mean when the uterus has sharp pains when you have sex?

Endometriosis: This is one possibility. The presence of this process/disease, depending on severity, has been associated with a symptom termed "deep dyspareunia." Essentially, the term acknowledges that the genito-urinary unit has become less pliable/elastic as it tries to undergo the normal physiologic changes associated with intercourse. The final outcome perceived by the patient is pain during sex.