Well it could be your gall bladder I had the same problem and had 2 get mine removed or just drink slot of carbonated drinks stretch and try 2 burp other wise please consult a dr. It also could be acid reflux . Please take my advice.
The best way to release trapped gas is to walk. Walking will usually clear it out. If you can burp really big that will help too. Try drinking something that makes you burp a lot if the walking doesn't help you out.
Try GasX or another generic version of simethicone. This just breaks up bubbles and allows you to burp or pass gas and relieve pressure. This stuff is pretty benign and doesn't interfere with many other meds at all. You can get it almost anywhere.