16 weeks

I'm 16 weeks tomorrow and it seems like for the last two weeks my uterus has hurt so bad. It feels like my baby is growing but my uterus isn't growing with it. There's so much pressure and at some points I can feel it in my back. My and my boyfriend were talking and thinking maybe it's the baby kicking but I just don't feel it from the outside yet so I don't know what it really is. Hmm. Any advice or anyone else have this?