Tmi...rectal pain

I am 18 weeks pregnant and for the last couple of weeks every once in awhile I get a sharp pain in my rectum. Sorry tmi. I was driving today and almost had to stop the car I was in so much pain. Then it hit again when I was getting out of the car and I could not move until it passed. I didn't have any gas nor did I need to have a bowel movement. I'm not sure what causes it or when it's going to strike. Has anyone else had this?