D.W.
First of all I never heard of a baby having an aversion to pooping. It sounds like she is doing better on the formula she is on. Try some mylicon or some other type of gas drops and see if it helps. She may grow out of some of this. She will probably do better when she can eat baby food. As far as the head rolling forward there are things that you can buy for example in target which goes around their head in the car seat for neck support. Another thing you can do is roll up a blanket and put it next to the side she is sloping towards. I remember being worried about it too when my son was young. It is hard going from one to two. I remember my one girlfriend who told me how hard it was. I wish you luck. You are doing great. You are just going through a period of adjustment.