Formula Milk

Good morning mga momsh. My 3-month old baby is mix feed with Similac but mostly, sakin sya nadede. Kaya lang napansin ko this past few days, hindi na sya masyadong nakaka ubos ng formula. Yung tipong kahit 2oz lang tinimpla ko (after breastfeeding) 1oz lang madedede nya samantalang dati nakaka 3oz sya ng formula after ko syang ibreastfeed. Btw, the reason i mix fed my baby is dahil hindi sya nabubusog sakin. Tried unli latch too. More than 2 hrs ko syang pinadede sakin pero pagkatapos nun gutom pa rin sya kaya ang ending, formula pa rin. Do i have to change his formula milk? If yes any milk suggestion? I was also thinking of pure breastfeeding my baby but he keeps on biting my nipples numerous times! Nangangagat na ba talaga ng utong ang 3mos old? Hindi pa naman sya nagngingipin. Ftm here. Thanks po sa mga sasagot!