help. I'm worried

My month and a half old has been throwing up. Or what I thought was throw up. He eats a lot a lot. I'm breastfeeding. Well, to me he eats a lot. Anyways, after he eats I'll burp him. And he will burp. But after white liquid will come out. It's more stringy like saliva. And it isn't constantly coming out right after the other like vomit. Just once or twice at most after the other. He doesn't seem to be in pain. He doesn't cry after or anything. It's just the amount that comes out. It's a good amount in my opinion. Is this vomit or throw up and how do I get him to stop? I was told it could be acid reflux and to sit him or hold him upward for 20 minutes but that doesn't seem to help. What is this?