I would say your frog is just taking longer to get used to it's new enviroment. When I got my African clawed Frogs, one always used to eat more than other and it tended to switch between the two. I fed my frogs on frozen blood worm, half a block between the two. Only one survived but now he is fully settled and eats a full block to himself!

I would say carry on feeding pellets but try other food with it, I got recommended using tubifex or californian blackworms (I think it was called that you will have to check) they have nutrition in them, so if your frog isn't eating a lot, at least it would still be getting the nutrition it needs.

Good Luck