I Am Having Bad Coughing Attacks Lots Of Frothy Foamy

I am having bad coughing attacks lots of frothy foamy mucus I had a sinus inf 3 wks ago antibiotcs amoxicillian high dose for ten days when done I had foot surgery 6 days ago was put to sleep with propothol seemed ok until today it last about 20 min I used a cough syrup and 2 puffs of inhaler better now the cough is not as bad now tomorrow I have stitches out what could this cough be I thought I was going to dye