Why won't my feebas evolve in pokemon diamond?

i've fed it as many poffins as i can but it still won't evolve!! i used ONLY beauty poffins so i dont know what's wrong...maybe because i gave it the exp. share so i didnt have to evolve it slowly? (im lazy...) i need a milotic so i can trade it on GTS so i can get a piplup. then if i can evolve it into prinplup my sinnoh dex will be completed!! help meeeeeee!! plz