I have been having olfactory illusions, a bad/sour smell for almost year and recently it lasted for several days, so strong that it made me nausious. My sinus was also congested with a persistent wet cough. My doctor put me on a course of Clydamicin for 10 days to rule out a sinus unfection. My cough was much better but my congestion is the same. I am experiencing allergies for the first time (I am a 67 year female, don t smoke, in reasonably good health), so maybe that is the source of the congestion, don t know. Could this smell thing be a symptom of a brain tumor or ???