H.1.
My son went through the same thing....it was a phase that passed, thank goodness. He just needed a few weeks to figure it out. Our big problem was that it disturbed his night time and nap sleeping - rolling on to his tummy would wake him up and make him mad! We always let him cry for a bit to see if he could sleep through it but usually ended up rolling him over. It was a tiring couple of weeks but he figured it out quickly - either got used to sleeping on his belly or learned how to get back to where he wanted. There's little you can do about this one!