I think I'm not suffering sinusitis because I didn't experience such facial pain and clogged nose.my sister is experiencing that symptoms.she is always having a phlegm specially in the morning but I didn't smell something like that from her.. if I'm not suffering sinusitis.. what could it be? I discovered also that this very unpleasant smell can be smelled several meters away from me.

Did someone else tell you that you have an odor or do just you notice it?

You could have an infection in your sinuses without the customary symptoms. You could also have some old food stuck in your tonsils or something. Another source of bad smells can be a dental problem - you could have a tooth or gum issue that you aren't aware of.

Go to a doctor and if they can't sort it out, go to your dentist.