HI. You can not see a sinus. What you are looking is at the nose. Your symptoms are suggestive of sinusitis
as you have rightly mentioned.
What you need is a proper evaluation by blood an other tests and CT scan
of the nose and sinuses
This along with the examination of the nasal discharge for microscopy, culture and sensitivity will lead to a proper diagnosis and further management.
The bubbles may result from an anerobic infection
You need a combination treatment and surgery if the CT scan is suggestive so.