Gracie, your levels depend on if you have been taking your medicine, sticking to the diet, and other factors (such as exercsing which helps keeps levels down). I have never heard of fasting before getting a level taken. I am 20 years old and have never done so. In fact, I usually take my medicine right before I go to the hospital to get blood taken. I don't know how high a level would go because of a breastmilk feeding since the change depends on the person's tolerance but if your child is regularly consuming breastmilk already and their levels have been fine then I do not see what the problem is.