You need to keep his day temp high. Low to mid 80°s and night time drop should only be a few degrees. If it drops too much your frog can become ill. Keep him at 80° constant for a day or so then try to feed him. To do this you will need to use a night time bulb. Either a ceramic heat emitter like Jimmi mentioned or an Infrared bulb. 50 or 60 watts is fine. Leave the heat pad on.

I also see that you don't have any sort of background on the tank. Cover 3 sides of the tank with some kind of terrarium background so he feels more secure. Substrate should only be deep enough so that he can cover himself not so you cant't find him easily.

Get a Hygrometer that is digital with a probe. Buy an Exo Terra dual combo. It has both Thermometer and Hygrometer built in. The probe goes in the tank and the gauge stays out.