I think you need to give him more time to settle in before you start forcing meds, even natural ones down him. How old is he? A dragon that size can easily go 1 week or longer between going to the bathroom. Try to handle him only for bathing, otherwise leave him be so he can get settled in.
Babies and juvies will go every day but adults usually don't. My big male only goes once a week, some times even longer. If I'm feeding mostly supers, he will go longer in between, if I feed silkies or dubia he will go a bit more often. Are you only feeding supers? You might look into silkies or horns, they are juicy and it helps move things along.
You could also give him a bit of baby apple food daily, that will also help move things along. He is probably fine though and will go when he needs to.