My ENT confirmed MRSA w/ bad sinus infection. Taking doxy-cycline gusing muciprin mixed w/ saline spray 4x daily. How contagious am i?

Not very. As long as you are on antibiotics and wash your hands after irrigations, those around you should be safe. Stay away from newborns, extremely aged, and those with impaired immune systems (chronically ill or cancer patients) just to be safe.