Spit up after feeding?

Hey ladies! So we had my little guy on Similac Advance from about 3wks until now, he's 6wks 3days, I called his pediatricians office yesterday because he was almost always spitting up not just after feedings and when I'd burp him but when I'd change his diaper and lay him down,hold him, or even sometimes when he'd be in his swing. They recommended I switch him to Similac Sensitive which I had a sample of, and he doesn't seem to spit up as much, but just wondering what's normal and what's not? They said if it doesn't get any better to call them back and bring him in.... Any advice is helpful, thanks