I have a tankfull of bottom feeders, so frog eating is competitive- if the food even hits the bottom. I had 2 die. I have 2 now that I think I will be removing from the tank to feed (sorry Leo, i know this is stressful, but all my other fish are way fat!)...point is you have to be really patient with the feeding. I use a turkey baster, the frogs go right to it, take a gulp, you have to wait for them to swallow before another...
If your frog is eating so little you probably want to try daily feedings or twice daily of 1 worm. It seems stressed if it isn't eating. You probalby have to do something that Leo suggested. Also have you tried different foods? BLood worms are mine's fav, but they also like brine shrimp.
Mine usually float at the top, "play" or accidentally fall into the wild ride of the filter current, try to grab onto fish fins it thinks is food, or chill at the bottom. They get really active and swim everywhere when I feed them- usually in the evening. They try and eat everything that floats by, and jump into the fish frenzie at feeding time. Other times they look dead. having more than one would probably boost the activity of your frog and once you get it comfortable in the tank too...it may take a week or 2 for it to settle into it's new home.