What are the actual temps inside the tank? Also, the humidity? The reason I ask is because heat pads don't provide that much heat, and it's very localized... I keep mine on as sort of an emergency heat source in case something happens and the room's space heater accidentally gets turned off or unplugged, so my frog can huddle up against it until I can correct the problem (happened last night actually...). A bulb is really better for heating.
Can you post the Trouble in the Enclosure sticky and answer all those questions including any changes you've made to his tank?

One thing about pacs is that they can hold so much water they can still look fat even when they are very thin. If you sit him in his water dish he will probably pee, then you can see whether he's really getting skinny or not.
Can you feel very gently along your frog's right side? Sometimes frogs will stop eating and pooping when they have a blockage called an impaction. If you feel a lump on the right side, that's what it is. To treat that, I usually soak the frog for 10-15 minutes in honey water.