Hello,
I am sorry your dragon hasn't been eating, that is a very common issue when on antibiotics.
I hope you are able to find some tomorrow. As suggested, be sure to get non dairy soy yogurt, if you do get some at the store.
You can try going to the health food store & they should have acidophiliz there also you could get.
I would definitely remove the sand, it is a bit dusty & can contribute to respiratory issues, too. You can just use tiles, non adhesive shelf liner or paper towels.
Let us know how he is doing.
Tracie