According to Everyday Health, John C. Petrozza, MD, board-certified obstetrician-gynecologist at Massachusetts General Hospital Fertility Center offers these tips for easing the pain during sex. Although they are geared toward endometriosis-related pain, they also may relieve symptoms in other situations: 

• try side-to-side or "doggy style" positions in lieu of missionary, which is the most uncomfortable position because of the tilt of the pelvis;
• pick the least painful times of your menstrual cycle to have sex. Most women experience more endometrial pain mid-cycle, so you might want to forgo sex during those few days;
• talk to your partner about the pain to keep communication open. Having him or her involved in what you’re going through can make you feel understood and avoid misconstruing your physical pain as a relationship issue; and
• consider kissing, fondling and massage as alternatives when there’s discomfort.