What causes really bad smelling gas that's worse than normal?

Gas: Very unpleasant intestinal flatulence rarely indicates any serious pathology and varies with certain foods. See if you can relate it to starches, sugars, beer, etc. Taking activated charcoal may alleviate the foul smelling flatulence.

Change in diet.: First thing I would think of in this context would be a simple change in diet. Second thought would be small intestinal bacterial overgrowth,, which could have happened from recent illness or use of antibiotics. Try some probiotics and see if they help to bring things back to normal.