Heat mats are a beardie no-no. They don't feel heat through their stomachs, only from above, so if it gets to hot they don't know and can get burnt. If your tank is getting that cool at night, get a ceramic heat emitter.
Switching light sides shouldn't hurt, he'll probably be taking a little while to adapt to his new surroundings anyhow.
Some beardies do brumate (hibernate) in captivity, but if he's moving around and eating it doesn't really sound like he is. This is a good article-
http://www.beardeddragon.org/articles/brumation/
Feeding... well, some dragons are finicky about greens, but if they're always availible and feeders aren't, they'll usually come around.
http://www.beautifuldragons.503xtreme.com/Nutrition.html is a very useful site for food. At a year and a half he should be eating 30-50 live feeders per week, with feedings every other day or so.
Pooping is kind of up in the air. Good eaters will generally poop every day when they're young, but adults usually start to poop less. My older kids only go 2-3 times a week.
If you like, you can fill out these questions and we can see if there's anything else we can help you with:
What type substrate do you have on the bottom of your tank?
Do you use UVB lights?
If so, Is it a coil, compact, fluorescent tube, or Mercury Vapor bulb?
What is the brand name and number of your bulb? Wattage (if MVB)?
How old is your
UVB bulb?
How close can your dragon get to the UVB?
Do you use a separate basking bulb? What kind and what is the wattage?
What are the basking temps?
What is the cool side temp?
Do you take the temps with a stick on thermometer, a digital thermometer with a wire and a probe end or a temp gun?
Where exactly are you taking your basking temps?
Do you use a heat rock or heat pad?
What do you feed your dragon? Please be specific.
How often do you feed and what time do you feed (morning, afternoon, night)?
Do you gutload (feed) your crickets, worms, etc?
Do you use vitamin or calcium supplements? What brand(s)? How many days a week do you use each of them?
Is your dragon having regular bowel movements (poops)?
Do you
bath your dragon? How often?
Do you mist your dragon or offer water other than in the
bath?
Does your dragon share an enclosure with another dragon?
Have you gotten a vet check and fecal done?