Is my 5 week old allergic to milk?

If you have food allergies in the family, it is very important to not give formula and exclusively feed. You have already done a lot of damage to your baby's digestive system by giving formula, but it would still be much better to get your baby to nurse again and exclusively feed, which is quite possible. Get in touch with a lactation consultant and a La Leche League leader to help you. You do not have to cut things out of your diet unless after you have been exclusively feeding for a bit your baby is reacting, then you can eliminate common allergens for a while and see if that helps. If it doesn't, you may have to do a full elimination diet to find out what it is that is bothering your baby.