By Eve Wagstaff Menstrual cramps can be very painful, forcing people to miss social events and take time off work. The standard ache that most women and people with uteruses have can normally be managed by painkillers and a hot water bottle but there are also conditions that can cause a person to be in agony. Endometriosis is when cells that normally line your uterus grow outside it in other parts of your body, and can result in excruciating stomach pain for the sufferer. Some of the symptoms, in addition to the pain, are being physically sick, feeling nauseated constantly, constipation, diarr…