Hello everyone! Could you please tell me if it's normal for my child to…

Hello everyone! Could you please tell me if it's normal for my child to sometimes push against one side, like hitting and then lying down briefly with their head pressed against that side? Then they let go. There is no pain on my part. I was sure this was normal and thought he was just playing around, but now I sit here and wonder what if it isn't ?. A doppler ultrasound was done a few days ago, everything is fine. I will have an ultrasound tomorrow.