2 month old Spitup from nose and choking

Hi, my son is 2 1/2 months now. He is having trouble with spitup since he was 1 month old. I have consulted 3 doctors already and they have suggested nasoclear to make sure it is not due to blocked nose or congestion. Also, I was asked to give neopeptine drops which also didn't work. We always burp him after feed and keep him upright in lap for atleast 30 mins after feed. I also make him sleep with his head and upper body little raised up. But nothing seems to work. His spit up comes through his nose and chokes him making it a very difficult to breathe. It happens even when baby and we are all asleep making it scary as we may not even know he is choking as the baby is not even able to cry. Please guide if any suggestions other than this.