Low Weight Gain

My baby just turned 4 months a few days ago. Pinanganak ko sya with weight of 2,523 grams. First 3 months naggain naman sya 1-1.2kg per month. Pero now nasa 600g lang na gain nya :( My baby is mixed fed (both in bottles, ayaw kasi mag latch ni baby since 3 weeks old). 3oz ng pumped milk ko + 2oz ng fm nauubos nya. Since 1 month sya Enfamil Gentlease na milk nya, hiyang kasi sa kanya talaga. Nag ask na din ako sa pedia and may silent reflux daw si baby ko. pero ang nakikita ko lang symptoms na connected sa reflux ni baby is yung may days talaga na difficult sya paededin - ayaw nya ubusin milk nya. Timbang lang ni baby now is 5.85kg. Normal lang kaya to? Anyways magstart na din sya mag solid by 5 months as per pedia's advise. 🥹 Sino po dito magka same weight lang ni baby ko? Ano po vitamins pinapa take nyo 🙏🏻