I share the same case before, with very thick phelgm as well. After consulting various doctor, there's no use and what they said was just alergy.
Well, seeing my son getting thinner and thinner, I use two "Hau Cho San" everyday for 6 days, then the in-between days I also took him to see the Chinese medicine and after everything stopped, I tried some "Dong Chong Cho" pills for him, though he still has a little bit cough in the morning and day time, his very very thick phelgm was gone away and he seems fatter than before as his appetite is not affected by the Chinese medicine.
I've asked the shop assistant regarding two "Hau Cho San" per day and he said if the case is severe, it's OK and it really works together with the Chinese medicine !!!