Could you describe the bad smell?
There are a number of digestion disorders that result in the inability to break down some waste products, causing these products to build up to abnormally high levels. This may cause a body smell.
Depending on the disorder, one may smell like ammonia, or like fish. Other smells are possible too, but I’m not an expert in this field, so I cannot provide you with an exhaustive list.
Skin and eye color (the white part of the eye) might change as well. But I think there are digestion disorders that do cause a smell without causing a change in the color of the skin or eyes.
Anyway, if you describe the smell to a doctor, he/she can order a simple blood test for increased levels of some waste product or byproduct. That would give you a clue as to the underlying disorder. Some of them are even easily curable – though some others can only be semi-cured by adhering to a strict diet.
Anyway, if you haven’t already done so, ask your doctor.