belly changing shape??

So I've noticed a lot today. That my belly will go hard and kind of flat on top for a few mins then go back to normal. While this is happening I can feel the shape of the baby and it's really uncomfortable but not painful. He is still moving around a lot which is also really uncomfortable the last few days. Any ideas what this could be. I don't think it Braxton hicks well I thought I was already getting those when my belly just tightens and dosent change shape like this.