J.S.
I had to supplement with formula starting in September, my son was about 8 1/2 months old. I had some samples of regular Enfamil and Similac that I had gotten in the mail during my pregnancy. He flat out refused the formula. I tried to mix it with breast milk, (and I hated to because I only was able to pump a small amount) and he refused that. Then the doctors office gave me samples of Enfamil ProSoBee and he drank that all down with no problem. The doctor said that the soy based formula is closer to breast milk than the regular milk based formula. So my advice to you is whatever brand you are using-see if they have a soy based formula, and try that. GOod luck!