Girls, hello everyone! My son learned to roll over from his back to his…

Girls, hello everyone! My son learned to roll over from his back to his tummy about a month ago, and then he's still not able to flip back onto his back. He keeps repeating that he will roll over to his tummy, lies down, then gets tired, cries, I put him on his back and within seconds he's back on his tummy. Even in his sleep he tries to roll over to his tummy. Is this normal?