Will he drink with meals in a sippy? Mine are starting to not want bottles. Whatever BM they don't drink I put in a sippy and they down it with their meal. I also offer whole milk.
Also, maybe try an open cup-see if that will work. I'd give it a couple days, as long as he's peeing as normal. It could be teething as well.
Try WCM as well, see if you can get that in him. I'd stay away from the juice, but that's just my opinion. I'd do water before juice to keep him hydrated if he won't take formula/BM/WCM.
Im breezy but I wouldnt worry too much. Talk it over with the Pedi but I would try to get him calcium in other ways. Miss R doesnt drink much milk. I think she was a tiny bit older when she cut back but now its only 1-2 little cups a day. She has been this way for a while. She loves yogurt and cheese.