I am a healthy active 49 year-old woman. About three weeks ago I had what I thought was a mild stomach flu, with nausea and aching but no vomiting. Since then, the nausea has persisted, on and off. I also have burping and my bowel movements are not as regular. I was taking calcium/magnesium supplements and thought that might be the culprit, so I stopped about a week ago, but no improvement. Any idea what this could be?