What Causes Unpleasant Odour In Nose After Surgeries For Breast Cancer And Back?

I have had surgery twice in the last six months. (Breast cancer and back disc surgeries.) Both times a few weeks after surgery I get this foul smell in my nose. Like I'm smelling something dirty. I'm going a little nuts looking for it on Google and I do have a doctor's appt scheduled. Do you know what this could be caused by? My email address is YYYY@YYYY