The baby is moving around now as he/she does not have as much room to move around in. If it is worrying You speak to Your doctor about it I would not panic though it is most likely just the pressure of the baby
Maybe you are feeling braxton hicks contractions, that could cause a bit of that pressure. It could also just be the way your baby is positioned in your belly...the bigger they grow, the less room they have and the more they push out and try to stretch out. If it's bugging you or you're in pain...make sure you talk to your doc about it.