I see you have wasted the time of being a member of such a great info filled forum.
First check out the caresheet. http://ball-pythons.net/forums/showt...ius)-Caresheet
Next I would upload a picture of the tank with as much detail as possible. Tell us what sources of heat you are using and how you have them set up. You say you may have a temp problem but didn't state any known tank temps. Its really hard for us to help you with the little you included.
I'm going to be general and take some guesses at what I think you are using in your setup.
Your temps need to stay as steady as possible. The air temp in the whole tank should be between 78-84, air temp is also referred to as ambient temp. Next you need to provide a hotspot of 88-91 with a under tank heater (uth). The uth needs to be hooked up to a thermostat (tstat) to regulate it so you do not burn your snake. You should have a thermometer to track your cage ambient temp.
The uth needs to have a very thin layer of substrate over it. Usually 1/4 inch is good. You need to know the actual temp of the cage floor over the uth. The tstat may need to be set above the target temp but it should not be but a few degrees more. Having a think layer of substrate over the uth does not allow the heat to reach the snake and then becomes useless. The reason you want to know the actual cage floor temp is in the event your snake moves the substrate and lays directly on the bottom you will not be dealing with a burned snake. The best way to monitor this is with a IR temp gun but a probe thermometer can work too.
Your trip to the vet and dealing with a dehydrated snake tells me your humidity is to low for long periods of time. You should be misting as often as necessary to keep your humidity between 40-60 while not in shed and 60-70 while in shed. Being that you need to track your temps and humidity many of us use a gauge that does both. This is it on Amazon but Walmart has them too http://www.amazon.com/Chaney-Instrum...words=accurite . Their are a few other methods of raising your humidity but we can help you with those when we know more about your setup.
The fasting could be from a number of things and the only way to know for sure is to get your snakes tank near perfect to narrow it down. It could be cold temp, time of year, security issue, stress, etc.
First feeding in a different container is not needed and not desired. All this does is stress the snake out by taking it away from its home. Feeding in is cage will not make it aggressive and you actually raise the odds of getting bit by moving a snake while in feed mode.
Next is security. If you moved it to a new large tank and it has large open areas try to clutter it up. Add plants, driftwood, branches, etc to give the snake cover and concealment. That will make it feel secure and reduce stress and make it more prone to eat.
Also going with security is its hide. The half log hides do not actually make a bp feel secure and a better choice would be this.
http://www.reptilebasics.com/hide-boxes
Their hide needs to be snug and have one door.
Now to help with getting your temps right we need the information on what your using and what you have available.
You have many issues but it is very possible to get it right. Help us help you.