Mommy, can you please tell me? My baby is 4 months old and we're alre…

Mommy, can you please tell me? My baby is 4 months old and we're already flipping him on his tummy, but he doesn't want to lie on his back anymore. He only wants to sleep in the stroller lying on his back. The rest of the time he sleeps on his tummy all night long. Now I have a question: When he lies on his tummy, does he lift his butt higher than his head, almost standing on his toes, pushing off with his feet, and getting upset? Does he want to crawl or something else? I'm really worried. We got massages, there was no tone at all. In the stroller when he lies on his back, he also tries to