PG is more of an irritant than the VG is. Coughing up the VG is a good thing. It acts as a carrier for any crud in your lungs from smoking. Try turning your airflow down a bit so you get less vapor per pull. Also any pollen, dust, animal dander, that might be bouncing around in there. You can probably tell the difference between coughing up mucus from the vg and an asthma attack? Does the vg trigger your asthma or do you find you have less attacks while vaping on vg? It affects people differently, so I'm just curious.