Constant fluid coming back into throat - help!

My GP initially thought I had gall bladder symptoms but now thinks its something else.  Hes put me on 40 mgs omeprazole daily (losec) but every time i eat I get regurg coming back into my throat instead of a burp!  Gross I know.  Its stained with brownish streaks. Im a coffee drinker so it could be that but still its worrying!  Its caused me chest pain central high and going directly through to my back between my shoulder blades.  Does this sound like GERD?  Im very confused.  Hes scheduled an endoscopy for me which will take about 4 weeks, but i would like to hear if any others have acid/fluid coming back into the throat, and more importantly if its stained! Thanks in advance