My baby has SO much mucus at 6 months

My baby is 6 months and has had congestion since being home from NICU. When we took our baby home our baby had congestion and then a stuffy nose a little later. He would spit up a lot and spit up even snot. Very often there’s snot in his spit up and it worries me. The pediatrician said congestion is normal and it’s because of babies small nasal passages. But like a week ago he spit up SO MUCH SNOT it was like 90% snot and 10% milk. It was so thick and sticky I thought for sure finally all of it is out. Nope still has snot in his spit up. I’m so tired of this I keep thinking he spits up so much because of this mucus. I had pediatrician listen to his lungs closely to see if he’s having trouble breathing because he has so much mucus I was worrying and wanted to make sure it’s not in his lungs. Anyways they say everything looks good and is good but still wondering why this is even happening. Half a year and still congestion! I can’t stand it. I’m so careful dress baby really good and warm. Baby is always cozy if cold outside. I’m so careful and I don’t know how baby has all this congestion. Anyone else have delt with this?