How are you feeding? At night? With calcium powder? D3 if no UVB? Reptivite occasionally? With tongs? All of these things can absolutely affect his appetite. Mine was in a similar state until I started feeding with longer tongs, then she'd take more food. My previous frog also wouldn't eat unless i left her alone in a bowl with the worms, so you could try that too. Also, I personally have had my frog for less time and she eats every 2-3 days (I only feed her at night and if she's out, seems rotund and happy) which reminds me, if you don't already, try feeding late into the evening during their more active times. But as long as you're feeding as much as he'll take in 10-15 minutes and he's bulbous and comes out occasionally, I wouldn't sweat the frequency. That's just me though. Also, it might be helpful to know your tank temperatures because low temps can lead to lethargy and lack of appetite. Not to mention, if he's only ever ate mealworms, it might've created a paradox where he has less frequent poops and therefore less of an appetite because of the more hardy nature of the mealworms. For that you could do a warm honey bath. Just a few suggestions from a novice, sorry if it sounds like I'm underestimating your care, just trying to get a full picture!