Able was on Nutramigen for the past 7 months because my milk was breaking him out while the last…

Able was on Nutramigen for the past 7 months because my milk was breaking him out while the last time we was at the doctor she wanted to see how he did with Similac Sensitive the first few days he did really good so we switch to it & now he WILL NOT take it he will take one drink and turn his head. I've tried to mix it half and half but he will not take it. What should I do? He will take just a plan bottle of Nutramigen. But I want him to get use to milk before he is a year old and doesn't get formula anymore.