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…

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