How to help my toddler poop?

Vous • Mom to 💙 Silas »061319«

He’s been pooping once every other day and I know that’s now how it’s supposed to be... Because he’s constipated, his appetite is very crappy, and every appointment that comes up, his weight isn’t improving.

How do I do this? They’re prescribing him Miralax to help him the medicated way, which I have to pick up today.