I have IBS but do not ususully have nausea. When I have had nausea, it was related to GERD or an irritated stomach and throat.
The best remedy that I have found for nausea is a homeopathic remedy --- Ipecacuanha 30X potency but any potency will work ---I just like 30X.
If nausea is caused by gastritis and sometimes it is--- a supplement given to me by a doctor works well. Mastica ---mastic gum is resinous material used by the Greeks for hundreds of years for GI problems. A study reported to the New England Journal of Medicine supports that it helps GI health. If interested you may be able to search and buy it online. The report I read said it was effective against H.Pylori bacteria but I think it does alot more. It did for me!!!