I don't get this very often, luckily, but when I do it can be uncomfortable enough to need painkillers and lying down with a hot water bottle. It's like period pain, usually in the last days of my period, or after the bleeding has stopped. Sometimes the pain is in one side, close to my groin. And today it was exactly the same place as a period pain. It can only be described as an ache similar to period pain, but more uncomfortable. It kind of comes and goes in "waves" and only lasts up to 30-60 mins. Afterwards I feel tired and a bit run down. Then I am fine for the rest of the month. As I say, it only happens a few times a year. Could it be endometriosis? I am 43, married with teenage children, who I had by elective caesarian.