tommygirl90us
Even though they are both enfamil I wouldn't switch back and fourth. It takes a baby a while to adjust between formulas and the way you are doing it he isn't having time on either end to adjust. I would suggest sticking to regular enfamil until it is time to switch. I had to switch formulas with my daughter and it was rough she would get sick every now and then it took about two weeks for her to get used to the new one.

parental unit
at his age there should not be an issue. He would be fine switching between brands at this age. Its only when they are really little with immature gut system that you need to be cautious