Girls! Hello. Please advise. Lately—though not every day and not inten…

Girls! Hello. Please advise. Lately—though not every day and not intensely—sometimes when I'm sitting I get a sudden shooting pain inside my uterus, like an electric shock. It happened a week ago on the road: we were driving to another city and I sat for 4 hours; we did stop about every hour, but it shot pains in my uterus and also into my rectum. What could this be? Is it stretching there? Thanks in advance. ?