How long does it take for cow's milk to leave your milk?

My son was just diagnosed with a Milk Protein Allergy (I just asked a question about having to cut dairy and soy out of my diet at few minutes ago) His DR said it takes at least 2-3 weeks for it to fully leave you and your babies system! They way we figured out that he had this allergy was from bringing in soiled diapers to his dr. They then did a test and found that he had bloody stools, along with his pain, crying, and spitting up that he does had a milk allergy! He also has acid reflux as well. Maybe the spitting up has to do reflux?! But it will take at least 2-3 weeks for the milk to be fully out of your system!