hi there is a really good website called thegeckospot.com that has brilll care sheets and everything u will need to no. Leopard geckos need a heat mat as they need to get heat from underneath to be able to digest there food. also how long have you had it they generally take a week sometimes more to adjust to new places and can go without food for a while as long as it has a fat tail it should be fine.
also and u keeping it on sand as it could become impacted ! I'll try and help u as much as i can but the gecko spot should have all the info u need