What causes blood clot from sinus infection . having sinus pressure no blood dripping only when blowing then coming out mouth from hocking from nose?

Sinusitis: With nasal and or sinus congestion/infection, rupture of tiny blood vessels is common. If the bleeding isn't very brisk, coagulation occurs in the form of small clots adherent to the membranes. When you forcefully blow your nose the clots are dislodged and flow out nasally or from the back of nasal passages and drip into the throat. Sinus pressure develops when mucus can't drain into the nose

Sinusitis with clot: The inner lining of the nasal cavity is fragile. When dried out or inflamed, the underlying blood vessels of the nose tend to bleed. An older bleed that has stopped can cause blood clots. Please visit a PMD for treatment of your nosebleed and sinus infection, to see if antibiotics are needed. Sterile saline drops for nasal irrigation can help relieve symptoms until then.