Just a wild guess (but I had this too) I would say is because whilst your uterus might not be that high everything else is starting to squish up that high...iykwim. If you are worried I would get them to check to see everything is ok. But I remember being shortwinded from around the second ultrasound. Oh speaking of second ultrasound...I probably missed it, but how did it go? Boy or Girl?

*hugs*
Cailin