Browsed thru all the suggestions and my preemie had rsv and still suffers from congestion frequently-going through a course of it with sporadic fevers now. Same thing as your son with the gagging and choking. Believe me-I know exactly how you feel, your worries, and frustration. These are not in order of importance or steps but are most of the things I can think of to help you off the top of my head and after skimming through others suggestions.
1. Like the breast milk for nasal drops idea-I'm going to try this one.
2. Give the Johnson's vapo baths to help clear breathing. Never used the vapo rub but believe in that one too. I have gotten an email about putting a generous amount on the bottoms of their feet and putting socks over them before they go to bed as well. Says it is more effective when placed in their area and absorbed through the skin.
3. Bulb sucker-bulb sucker-bulb sucker. Everyone is right about baby's can't blow their own nose and do it right before feeding. Your baby won't eat as much if it is a struggle for him to breath while doing so. I think people can over use this though also which could probably aggravate the nasal passages. So I try to minimize it to before feedings (as needed), first thing in morning and after bath in evening. Just try to keep it wiped often the rest of the day.
4. Breast feed more often-don't cut off your milk supply to him. It is still too important at his age and his main source of vitamins, mins. etc. Solid food feeding is merely for learning to eat table foods and not their source of nutrients right now.
Sippy cups: He may even be starting to teeth as my 9 month cut her bottom in at 8 months and the dr advised that teething makes it sore for them to suck so try sippy cups to get fluids in him. I took the stoppers out and hold the cup for her and this helps get some in her here and there to make me feel better when she doesn't seem to be taking in her norm from me or the bottle. Of course it is slow going but with help and patience I get about an ounce to 2 in her with a cup when I the anxieties over her intake. Make sure to put a bib on him or be ready to put in dry clothes cause upto half of what you put in the cup will end up down the front of him as once again he will be learning to do something new.
5. Tylenol/Motrin. UGH! don't O.D. your baby. You can alternate the two but only every 4 hours. NOT 2-3 like someone said. Your pediatrician will concur on that one as this is what mine advised. Make sure you are giving the proper dose for your son's weight-too little will not be effective of course and once again we do not want to O.D. I found this last go round that I wasn't giving her enough-She is growing so fast.
6. If your baby has not been tested for RSV, he should be and if you are not comfortable with your doctor seek another opinion. My daughter as mentioned had RSV but the congestion lingered much longer than the norm and her original doctor continued to be passive of it. I took her immediately to a new doctor upon our move and they found she had a sinus infection that was dripping down the back of her throat that was causing the nasty cough and congestion. It was treated and gone within 5 days on ammoxycillin (don't know if that is spelled right).
7. Crib wedge-keeps him elevated so may be able to get some better sleep at night.
8. The cool mist humidifier is a good suggestion also but has not been one of our techniques on account that our daughter is still in a pack-n-play in our room while we are going thru a moving nightmare. My husband thought this made him sick when I used it once during my pregnancy due to a sever sinus infection I got and couldn't/wouldn't take any drugs for.