Eaten onion yesterday . from that having gas and it feels like food has not been digested still having taste of onion im mouth and had fever also.help?

Possible stomach flu: Itt is possible that the onion is not really causing the problem. It is possible that you have a viral or bacterial intestinal bug, causing indigestion. When people have the 'stomach flu' they notice bloating, gas, belching, and feel like their food is not digesting well. If you've had this reaction in the past with onions, then you clearly should avoid them, since you don't tolerate onions.