I think you need to go to the hospital and get checked out. I had a similar thing when I was pregnant with DS. They never found out what it was, but I went into labour a day later. Good luck!

Also... I went to the hospital with various weird conditions during both pregnancies, none of which resulted in anything, but the midwives always said that they'd rather have me come in and get checked out and it be nothing, than stay at home for a few days and it be something and having something bad happen.