The Enfamil (or any formula) with Lipil will probably make your baby sick. If you are breastfeeding exclusively, that would be the healthiest choice to continue. If you have already switched to formula, I would see a lactation consultant about your chances of relactating.
My pediatrician told me to suppliment with formula because my daughter wasn't gaining enough weight and I told her to go to hell. Have confidence in your milk supply. The more your child is at your breast, the healthier he or she will be. My daughter is still skinny (I was, too, as an infant), but she walked at 10 months, talked in complete sentences at 2, and she's never had an ear infection, asthma, diabetes, problems with spitting up or anything else that Formula can cause. I'm always shocked that women don't know that baby formulas contain Iron to counteract the intestinal bleeding it causes in your helpless infant. I became a stay-at-home mom to ensure that not a drop of formula would ever sicken my babies. We can't afford a 2nd car, vacations, getting take-out or many other things on our budget, but at least our kids are healthy.