I , too , have a very sensitive sense of smell- I pick up on the strangest odors that no one else notices. I had a terrible chemical sensitivity some years ago which still lingers with certain chemicals - it seems like the sense of smell is magnified. Sometimes it is overhwhemingly distracting.
I have read that there are cases of loss of smell, distorted smell - it has something to do with neurons in the olfactory . An interesting read on this and other senses by Diane Ackerman - " A Natural History of the Senses".
I do not think it is always clear as to why the sense of smell diminishes or distorts.
I was diagnosed with firbomyalgia in '96...a year after a nasty overexposure to chlorine. I always felt it affected my sense of smell was by sharpened by it. ( Or maybe my imagination !!)
Recently, though, taking meds for Lyme , my sense of smell ( and taste which is related) was totally off .
I have such bizarre happenings since this ll began that I try to humor myself about it - or it would drive me crazy!!