GERD with no heartburn or reflux

I’ve had chronic burping for months (sometimes nonstop all day), some nausea after eating (occasional vomiting), and stomach and abdominal pain. I’ve also had some chest pain occasionally. I had some standard blood tests and an X-ray and CT (to rule out appendicitis) and they were all negative. My doctors told me it was GERD and I took Zantac for a few weeks, it didn’t help at all. I’ve been taking omeprazole for a few weeks and it also hasn’t helped at all. If anything, things have gotten worse. I’ve had heartburn maybe once or twice in the past two months and barely any acid or reflux sensation, even before the medication. I occasionally have a metallic taste in my mouth when I burp but no vomiting blood or anything like that.