My son is 2 and half years old and he still drinks milk in bottle. He drinks water and juice in glass.?

he refuces to drink milk in a glass or sippy cup. We tried almost all the brands of sippy cups and glass.. but he is so stubborn and never drinks milk in them. When we stopped giving him bottle, he stopped eating everything for 4 days and started losing weight so badly. He is okay with water and Juice …