Excessive spit out

Hi All - My LO has been spitting out almost after every feed even after we sit him upright for about 30 mins. At first , we thought due to overfeeding but he's only 3 weeks old and barely finish 60 ml during feeding. He was warded to KKH before due to excessive spit out. All they did was monitor him and discharge after 2 days. I just fed him formula milk about 20-30 ml and burped him. Put him down about 5 mins and he spit out almost half of it. Worried mummy 😭😣