My Baby Changed From Novalac 1 To Novalac 2 Because

my baby changed from Novalac 1 to Novalac 2 because she is 6 months now. for the last 2 week since we have changed she is soooo constipated, I have tried prune juice, olive oil, brown sugar. we are on day 4 now and she cries and is red in the face but nothing. what can I do, will milk of magnesia help and how much>