Unfortunately, as nurses, we can't suggest something very specific. I would suggest that you see your GP about it. Sometimes they check for infection, and/or refer you back to a hospital lung respiratory team for a new assessment. Coughs can sometimes be due to acid reflux not related to lungs, so your GP may consider that. Some medications can cause a cough as a side effect.
If infection is not the issue, then sometimes doctors prescribe a course of oral steroids to dampen down any lung inflammation. There may be different inhalers as well to consider.
