Need Help Please!!!

am I first time mom! my baby is 3 months and a week. He usually drinks 6oz of milk he did breastfeeding only the first Month but since then he drinks formula with no problems but now since a couple of days he is bearly eating.. he drinks and ounce of 2 in the day and in the night hes a sleep eating he drinks like 3 oz or maybe 4 but he's not eating like he use to all of a sudden he just don't want he push the bottle away I change his formula cuz I thought maybe it will be that but no... any suggestions!! plz