I get all sorts of weird and wonderful uterus pains and I'm only 17 weeks. I reckon it's often just random growth spurts although my bubs would be quite a bit smaller than yours at the moment.

I've experienced growing pains since day dot so I'm use to them but I did have a few ouchy ones the other week that hurt while I was walking around. Every time I mention it to my OB he reminds me about the ligaments and how they're like strings holding onto the uterus - like a hot air balloon - and will stretch and hurt now and then. When I think of his analogy, I always feel better about it.

Not sure that helped you mcuh but know that you're not alone with the pains!