I used to get this too - saw your other post about burping. Have you tried pamine forte? I've been on it for awhile, and had tried stopping it for a bit because my doc thought it might be contributing to something else (dry eyes/mouth). I stopped it and was in constant pain because of the gas. Started back up and the gas pains stopped. Also, have you had a gastric emptying study (you eat some radioactive eggs and they watch how fast it moves through your stomach). Delayed gastric emptying caused me to feel naseous all the time (plus regurgitate most of what I ate)...i take domperidone + a digestive enzyme to help with gastric motility and my nausea is a lot better. There are lots of other explanations too, but it might be worth asking your doc for the test if you haven't explored it yet.
Everytime I have an attack of IBs, I have nausea, and lots of gas and burping.........Very uncomfortable, peppermint helps and so does celery , however not to any great extent