Hi, Thanks for query. The symptoms descibed you indicates that your son is probably having uncontrolled asthma. You also mentioned about green/ yellow phlegm which is suggestive of infection resulting in exacerbation of asthma. As you told he is having the symptoms despite having dulera( formoterl-mometasone) so shifting to foracort (formoterl-budesonide) or seroflo ( salmeterol-fluticasone) may be a better option. Oral Predsinolone should not be used on a long term basis . It will make asthma dependent on steroid as well lead to many systemic side effects. There are many causes of difficult to control asthma. The diagnosis may be wrong, the technique of inhalationa may be wrong. You should consult a pulmonologist. It is not wise to guide the treatment withot seeing your son.Hope, I satisfied your queries.