@reneemc - When this happens to me, I try doing my airway clearance "upside down" - literally. I will go into the "downward dog" pose, or alternatively, bend forward from the waist as if trying to touch my toes, and huff cough. I was out running errands today & had that issue. I stopped beside my car in a parking lot and bent over - 3 coughs and I got the gunk out.
Have you tried it?
Sue
PS By bending forward, my doctor assures me there is not danger of aspiration into the lungs.