There is nothing wrong with your frog's tongue. It is sticky and gets covered in dirt when it s misses and they don't like that, but they will just swallow it. Your frog sounds very under fed. You shouldn't try to feed it one at a time. Cover like 8 to 10 in calcium dust and put them in the tank. Your frog will not chase one cricket until it gets it, because they are ambush preditors. They eat what crawls in front of them, so the more there are the more likely it is for one to cross its path. I would give it a small mouse once every month or so as well. That is where they get they're main protene and calleries from. But don't feed it to many mice per month.