If operated upon,pyloric stenosis will NOT recur. The commonest cause of vomiting or spitting up milk at this age is regurgitation due to overfeeding. Feed the baby at a gap of atleast 3 hours,don't wake him up for feeds,burp him for 10 mins after every feed. After burping,lay him on his right side for half an hour and then keep him elevated by placing a cushion beneath the head and shoulders. If not improving,consult your paediatrician.