Sensitive formula worse than the regular stuff?

My first daughter needed Similac Sensitive formula so we went straight to that with our second. She has been so fussy and gassy and constipated so we switched to the Pro Comfort and that was even worse. We decided she might have a milk allergy so we tried the Alimentum but yikes that was the worst yet! So I told my husband we should just start over and go to the Similac Pro Advance and three bottles in she is doing really well. Is it possible for a child to react worse on sensitive formula than regular formula?