Tooth fairy - I echo what the other ladies have said regarding PS. My husbands half brother (three years old now, FIL and his new wife had twins) had this condition. He was losing weight for a few weeks and very very unhappy. It took some time for them to diagnose it, but he would projectile vomit almost every feeding. They thought maybe reflux and finally figured out it was the blockage. If your son is happy and only doing this every once and a while then unlikely to be PS. If it is developing, it won't be sudden or an emergency surgery.
My LO will have big spit ups occasionally (maybe one or two times a week). The most helpful thing I read online is that from our perspective it may look like a big spit up and we may think they are losing their entire meal.. But really may not be that much. They suggested taking just a tablespoon of milk and spilling it. It looks like a lot but is really just a tablespoon. If LO was really spitting up the entire meal, it would be a huge mess