When is spitting up considered a problem?

My little one is 2 1/2 weeks old and has been spitting up from day one. It's not just right after eating, sometimes a couple hours after. It's getting to the point where I can almost tell he's going to spit up before he does. He gets really fussy, squirms a lot, and starts arching his back. He seems to be gaining weight just fine it just appears that he's in pain when it happens. Which just breaks my heart. Should I be concerned?