My son is 5 weeks old and gets really congested at nightime.?

I always put him on his back in his crib or basinette abut this seems to make the congestion worse. He gulps, gasps and makes choking sounds ... sometimes stops breathing for a few seconds before the horrible scary noises come on again. I've tried propping his matress a bit so gravity might make the congestion ease up. It doesn't seem to help. Needless to say no one gets any sleep from either the noise or getting up every 5 minutes to see if he's OK. Having said this, after feeding him last night on the couch, I propped him up into a sitting position and put the nursing pillow and blankets all around him. He fell asleep just fine and there were no signs of the congestion. My Dr says that there is nothing to worry about and that th congestion isn't in his lungs and that he'll grow out of it ... it's been 5 weeks. Has anyone ever had a similar experience? BTW - this is baby number two for us. Baby number one made crazy noises too but not ones where we thought she wasn't going to wake up!