DH started supplementing with Similac for Supplementation a few weeks after I went back to work as I'm not pumping enough for R. Last week (a week after he started) we noticed she had hives all over. We finally figured out that it was the formula so the pediatrician told us to try a soy-based formula after waiting a few days. Today was R's first day on soy formula and we already noticed a possible rash. We will have to see what happens tomorrow. Which type of formula was your LO on?