Wow I was the same week as you when I got that pain! I went to doctors he told me its a muscle pulling I'm a little over 20weeks now and I'm still having problems with it :/ take warm baths and use heating pad on low if its getting to the point where you can't move go to your doctor that's what happen to me and he gave me something that helped
wow im same weeks as u and i felt the same thing lastnight hopefully we can get some answers!! if u do let me know please!