You didn't say if you'd been diagnosed with GERD or if you just thought you might have it.
Yes, make an appointment with a doctor. GERD can affect many things in your digestive area and loss of appetite along with an upset stomach can be indications of several different things. I can't make diagnosis because I'm not a physician, but I have learned that overgrowth of bacteria in the intestines can cause gas inside you that you may not notice, but will make you feel full therefore creating the feeling that you aren't hungry. I've also learned that many people with GERD suffer from appetite loss. If it happens once in a while, I would think it's just "one of those things". But if it happens regularly, then by all means make an appointment to find the cause. It could be something really simple to resolve, but you'll never know until you ask a professional.