That's a very tough question. Here is how I judge - if my sputum turns yellow, green or brownish, it's not asthma or Bronchiectasis. If I have a fever I suspect MAC or another infection. If it's chest pain, increased coughing or shortness of breath, I trynall the tools in my asthma/bronch toolbox, and if they don't help, I call the doc.
For example, two weeks ago I had a pain in my lung, especially with ANY exertion. Before I assumed it was MAC rearing its ugly head, I added an additional dose of my levalbuterol inhaler every morning with my Bronchiectasis inhaler. Opening the airways before the second inhaler made it more effective, and after a few days the pain went away. Still short of breath when chasing with the grands but not the pain.

Side note: wearing my facemask when out in the cold has kept me from cold-induced asthma attacks.
Sue