Why does my pacman frog keep flipping upside down?

For the third time today I walked into my room to find my baby pacman frog flipped over on its back. What can this mean? I've been consistently maintaining the temperature/humidity according to what the pet store recommended. I just bought him a couple weeks ago and he has never been very active. Usually just buries himself and sits there. Yesterday was the first time I noticed him being a bit more active and now he keeps fipping over! I've also yet to see him eat a cricket since I've had him...but I hear that's not overly uncommon? Any suggestions as to why he is flipping and if it's serious would be greatly appreciated. Thanks!