Rosemary's Baby: Why did Rosemary keep drinking the milk?

In Rosemary's Baby, Rosemary notices that the milk Minnie gives isn't good for her; she stops drinking it, and the pain she's been having stops. Didn't she notice the connection? In later scenes, we see her drinking the milk. Why? Why didn't the pain come back? Does it have anything to do with the fact that Minnie starts giving her cake, too?