Sayang, soalan ni kena tanya paediatrician atau surgeon dia first-first, sebab setiap baby different especially after surgery macam ni. A few of my mum friends yang babies diorang ada similar issues, doktor diorang yang recommend specific formula based on baby's condition, bukan kita boleh decide sendiri. Could be hydrolysed formula, or lactose-free, or something else entirely depending on what his intestines can handle now. Please jangan delay, call the hospital or clinic where he had the surgery, they should guide you on the best feeding plan. This is really important for his recovery!