Its quite possible that you are experiencing the smell sensation that occurred when your body absorbed substances that are now being mobilized and eliminated from your body.
In other words lets say you were around a strong smell of paint at some time and your body absorbed some of the toxic fumes. When those residues of fumes are moving out of your body you can actually re-experience to some degree the moments when you smelled and absorbed the paint.
So the smells that you are experiencing can actually be from memory.
You can probably remember the smell of turkey at a thanksgiving or the smell of fresh flowers in springtime if you try and not be there to smell them. These are from memory as is the possibility that the paint smell is from memory also. The difference being that you aren't trying to remember the smell of the paint, the residues from that paint being mobilized is triggering it for you.
So in reality its just from memory and it is a good sign that some stuff is being removed from your body that your better off without.
The other possibility is that you are actually smelling stuff in your environment because the sense of smell is greatly increased.
If you can rule that out then I would suspect the above which is what it sounds like.