The week I found out I was pregnant (week 4), I experienced that leg crease soreness as well. It would switch sides a bit, but I believe it was mostly on the right side. I was literally chalking it up to too much yoga--it just felt so overstretched and sore. I just kept rubbing it and for some reason, trying to stretch it more. As much as we were trying to get pregnant, I didn't even associate it. Then after I got the BFP, I read someone else's posts and they had the exact same thing the week they found out. So, I think it's just a stretching deal!