Same here, although it was so gradual it took me years to notice. Also I can smell some things even if they're relatively subtle, but only for a second or two. Then nothing at all.

I know that human sense of smell gets used to constant sensation and ignores it. Apparently, mine just does it super quickly. I learned to trust my instincts, because usually the ability to smell something goes away before I notice it consciously and I can't just smell it again.