L.G.
If the problem continues - (as it did with my son) - a little prune juice in every bottle helps (start with 1/4 oz and increase as needed but remember, it generally takes 3 days for what goes in, to come out, so don't get frustrated if you don't get immediate results. We switched to similac from enfamil because it was gentler on the tummy, and it helped a little, but the prune juice did the trick for us. I've also known people who've had to use Karo syrup, suppositories, and many other things. Constipation is very common in babies - breastfed or formula fed. just be persistant. Just an FYI - my son (almost 3) still has to drink 2-3 servings of juice a day to stay regular - so this may be something that will be with you for a while...