I have quit vaping for about 3 weeks now. why do i feel shortness of breath ?

Hard to know. The two issues may be unrelated. What you were vaping may have triggered changes in your lungs that are now showing up. You need to be evaluated so a diagnosis can be made, and treatment started.

Vaping and smoke exposure is associated with pulmonary inflammation and often with cough and shortness of breath. Other causes should be considered, including infections and cardiac conditions. Please request a Pulmonary referral from your physician. Pulmonary function testing and a chest x ray may be indicated.