Signs

What are some signs to stop giving-my son dairy milk ?! I recently started doing half formula and half 2% dairy milk so I can get him used to regular milk . My mom gave him one full bottle of just dairy milk and he drank it . I asked my sons doctor for his one year check up how can i start introducing milk to him and he said i can do half and half or one formula bottle and then one dairy milk for the next but i forgot to ask him what signs should I look out for if its not working out . Yesterday his poop smelled different lol like actual baby stinky poop and it was all watery . Pls help lol