Ornate Horned - Pac-Man Frog issue...?

Maybe he is simply tired of the same food and that is why he is eating less. See if you can alternate giving him crickets with either some other type of live food, or an appropriate (possibly 'dry') food designed for your type of frog. Since your frog has not improved with the warm water, it may be his diet that has him bored. If you suspect that the temperature may be bothering him, you could get him a larger tank and then keep a small light/ appropriate-sized heating lamp on over just a section of his tank. That way, he could move from darkness and dampness, to drier conditions with some warm light, all without having to rely on you to move him. I think both of my suggestions may help his well-being in general, but I wouldn't rule out taking him to the vet. There may be some infection or something else wrong, not necessarily the bowel problem.