Feeding a Baby

My 5 mos. baby is currently on a mixed feeding (breastfed and formula fed). Then this week baby does not want to be formula fed. Formula milk intake: Ex. 3 oz. Milk before and now: 1 oz. Milk. Breastmilk per boob is 1 oz only sometimes 2 oz. Worried mama here..what to do?pls. Advise Tia..