You are taking asthma medications and they are not helping
If you have been prescribed inhalers, such as a quick-relief inhaler and/or a controller inhaler, and they are not working, you are likely experiencing something other than asthma.
You have shortness of breath but no chest tightness or wheezing
Though shortness of breath alone is a common symptom of asthma, wheezing and chest tightness are also classic signs. Sometimes even with all three symptoms, asthma is not the correct diagnosis, but it's a reasonable place to start with testing.
Prednisone doesn't help
If your doctor gave you a course of prednisone (a steroid pill) and it hasn't helped, that is unusual for a person with asthma. Another condition is likely causing shortness of breath.
You have a BMI greater than 30
One study showed that asthma is more commonly misdiagnosed in individuals who are obese. This could be because people who are obese are more commonly short of breath.
Your doctor prescribed medication without giving you a PFT
If your doctor diagnosed you with asthma and prescribed medication without actually giving you a pulmonary function test, you may not really have asthma. A pulmonary function test can definitively show your doctor if you are experiencing asthma or not.