Underweight Breastfeeding baby..Help momsh

Mommies Help! 3 months nasi baby pero 3.7kg padin cya. 2.7kg birth weight nya.exclusive breastfeeding direct latch everytime anytime n gusto nya. Nagmamalunggay capsule, M2 at masabaw nmn pagkain ako pero sobrang baba ng weight gain. Sinubukan ko iformula pero ayaw nya. Your advise will be appreciated. Salamat in advance...