Thank you for clarifying,
As you may know, asthma
symptoms tend to be worse at night.
Most likely, the whistling is either due to your asthma or it is due to mucus buildup in your airways.
If you cough and that clears the whistling for a bit, then it is more likely to be mucus.
When asthma symptoms are starting to increase and you are needing your inhaler
more than twice per week or you are having nighttime symptoms three to four times per month, it is time to add a steroid inhaler if you are not using one.
I would follow up with your doctor so that he/she can assess your asthma control and listen to your lungs
You can also try using a mucus thinner such as Mucinex to see if that makes any difference for you.
Please feel free to ask any follow up questions,
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