These frogs do get alot bigger than Pacmans, males usually get upward of 9". As for your Pacman could it be a male? Male Pacmans are alittle smaller than females so that might explain the slow growth.
Anyways I feed mines: smelts from grocery stores, nightcrawlers, lobster roaches, crickets, and a mouse every month.
BTW the last pic females in container to left, male on right.