welcome to Healthcare Magic.
From your query it is not clear about source of bad smell. This problem can occur due to psychological or medical reasons, which need evaluation.
Any smell without source can be due to olfactory hallucination
, which can occur due to psychosis
, seizures or some intacranial lesions.
In such case you can seek consultation from psychiatrist
. You may also require investigation like MRI Brain.
Wish you all the best.
Dr Ashish Kumar Mittal