Phantom Odor?

Two months ago my fiance and I moved in to an apartment in an older building. From the first tour I smelled something off in the apartment. He did not, and when I brought up my concern to the Manager he seemed dumbfounded as he did not smell anything either. He assured me the carpets would be cleaned and that should take care of the problem. Sure enough, upon move in day the smell seemed to be gone, but the windows had been left wide open to air out the carpet cleaning smell.

It wasn't long before the smell came back. No one visiting the apartment seems to smell it, nor does my fiance, which seems odd because the odor is so pungent to my nose. Before someone suggests mold I will say, I have lived in moldy apartments before, this is not that smell. My best description is a musty old person smell.

The odor has gotten to the point that it is giving me migraines and I can't relax in my own home. I would open up windows and air it out, but I have bad allergies and live in the highest pollen count region of the western half of the U.S., and pollen is also a bad migraine trigger of mine.

Has anyone struggled with bad odors no one else can smell? Anyone have any suggestions for getting rid of the odor? We have a year long lease so moving is not an option.

Help!