4 week old baby having a lot of gas and fussiness?

She was on similac advance but i switched it to gas and fussiness couple days ago and now she keeps having gas and in pain is it cus i switched it? Well its funny cus its for gas but it makes her have gas! What should i do? Besides doctor i want ur opinion. Shes also eating 4-5oz every 3 hours! Sometimes she wants more! Normal?