So my son seems to always spit up if he's laid flat on his back and sometimes he will like mouth a…

So my son seems to always spit up if he's laid flat on his back and sometimes he will like mouth a gag but nothing comes out almost like he swallows it before it comes out...does this sound like it could be a reflux problem? He's got a Drs appointment tomorrow and I'm going to bring it up but I was just wondering what you guys think? Also sometimes when I try to burp him he will stiffen his legs and arch his back and cry until I put him back on my breast after I get a burp out