I suggest that you ask a family member or a close friend to determine if he/she smells the same odor and then if he/she can detect it from any part of your body.
If not detectable by another person, then it is most likely what is called Phantosmia. That is perception of smell without an odorant present in the environment The etiology of phantosmias is most often associated with a specific URI, head trauma, or the aging process but can occur at any time in one’s life. The cause is usually not found.
This type of problem occurs most often in healthy individuals. However, it can occasionally be associated with a number of diseases, so that should you have or develop other symptoms of any kind, it would be wise for you to check with your doctor. And, as many drugs, including herbal medication can cause such odors, you should check with your doctor regarding any meds you may be taking.
Long term studies have shown that phantosmia of unknown cause improves or disappears in almost two thirds of the patients after more than 5 years, and seems to be more likely a harmless symptom rather than a reliable predictor of early Parkinson's disease or other severe diseases.
Good luck,
It could be a form of epilepsy - you need to see a neurologist.
Btw I'm not fat so that's not the problem