What are the signs of the umbilical cord slipping?

I am 31 weeks pregnant and I have been having this weird pain or sensation in my cervix. It has a stinging feeling that starts at the top of the pelvic region and shoots straight down through my cervix or l area all the way to the opening. I do have some discharge but not enough to make me concerned. However I am concerned about this feeling. I have had it steadily all afternoon & evening today. I also read that I should call the doctor if the umbilical cord is slipping into the cervix or , but I don't have any idea if that is what this is or if I am being over paranoid. Please help if you can. Thanks