Help my son is 13 months and he won't take a bottle

Okay I need help. My son is 13 months now and he refuses to drink milk(of any kind) from a bottle or sippy cup. He will drink water from a sippy cup but not breast milk, regular milk or formula. I would really like to stop breast feeding and I will need to go back to work so it needs to happen but he won't do it. He just throws the bottle. At this point he should be on sippy cups so is it even worth getting him on a bottle?! Please give me ideas and help me out!!