I have the same issues, I haven't eaten gluten in 18 months, and stopped eating dairy two weeks ago to see if that would help. I don't eat red meat or pork ever, I only eat meat twice a week, I live off vegetables, tofu, and potatoes & rice, so all the people who say it's just that type of diet may be missing something.
I'm suffering this same problem right now; it started yesterday. When ever I get it, I usually lay off of eating for a day and let my digestive system bring itself back into its normal regulation. I've read that the problem could be from eating too much protein and fat. It started last night after devouring 2 healthy portions of fairly marbled chuck roast. Honestly, it was worth it; the roast was excellent. So, today, I'm drinking water and have already skipped breakfast. I'm still burping, but it's decreasing. Some people say you should never fast, but I disagree. Sometimes we get carried away with our eating, and fasting can help bring the body back into its normal regulation. Hope this helps.
I was told that one cause is gastroparesis. The doc has me on reglin to stimulate the stomach muscles. So far so good.
Get tested for H. pylori, a stomach bacteria that can cause the problem. It also can result in stomach acid problems.