The drainage is probably from a condition called "vasomotor rhinitis (VMR)". This is common in people with vascular problems, as it is a vascular problem in the lining of the nose and sinuses. When there is increased blood flow, there is increased drainage. Most likely, this is coming from your sinuses and therefore drains down the back of your throat and not out of your nose. A couple of things might help. First get a CT scan of the sinuses to be sure there is no infection. Next, I would suggest a trial of oral steroids for a short period of time. If this is VMR, it will go away for a while, but unfortunately come back. At least it will explain the problem. If it is VMR, increasing the inhaled nasal steroids sometimes helps a little, but there is no way to eliminate the problem as long as the basic condition persists, in your case lupus.