She may need to be fed more often. My DD has always had a bottle every 3-4 hours but at night it was every 2-3 hours.

And you are not a bad mummy. Its all trial and error with babies until you get it right. My DD didnt like s26 gold so changed her to novalac and she has less but its more filling for her and she has really im proved since being on it. She used to be very windy on s26 and we tried her again on it jsut recently as novalac is quite $$ and its still making her windy.

Just go with your instincts if she is hungry give her some more or up her bottles.