Bingo! It was the Fruit Loops!!!

You may have candida...or have trouble digesting wheat or milk (assuming you used milk). Any of these could account for the flatulence and mucous. Do some self-experiments with your diet and see how you feel and respond. Eliminate ALL sugars for a couple of weeks and make note of your experience. Then do the same with wheat and then milk. You want to eliminate them separately so you can determine where the problem lies. It is also possible that more than one of these is the problem. Once you figure out what the problem is, then you can address it.