Should I Be Concerned About My Infant S Low Weight, And How Can I Ensure He Gets Enough Milk While I M At Work?

Hi Dr My son is 10mnts old weighting 8.4kg he looks thin, his birth weight was 3.4kg. He eat too much to a point I wonder where the food goes. He doesn t like formula, I tried giving him Nan, s26, lectotigen he only wants breast milk. I tried expressing milk for him his still doesn t take it he wants straight from the breast. I am worried that because I spend most my time at work he is not getting enough milk and his weight is low.