It is normal, at least for me it is, I assume for others too unless it is accompanied by other symptoms such as spotting I wouldn't worry about it. I am fairly certain that it has something to do with the hormonal/physical changes going on in that area. I have always experienced this during ovulation, and when I am about to start my period it just became more frequent and unpredictable during pregnancy. Now it has seemed to relax, but I just get booted in the cervix by my baby instead lol.