I have been feeling like i can't get enough air. i quit smoking 15 days ago because of it. is it anything serious? i also have thyroid and asthma pro

Very well could be: Serious. Please check with your doctor asap!

Possibly: Smoking is bad for you, particularly if you have other pulmonary problems such as asthma. It is likely that if you do not start smoking again and take care of yourself this will resolve. However, it would be good for you to discuss this with a doctor that knows your medical status.

Fresh Air: Fresh air is excellent for keeping us healthy. Some folks, however, have an anxiety disorder that leads them to believe that they are not getting enough fresh air. If that is the case for you it is treatable with the help of a clinical psychologist. "hope and help for your nerves" is a good book to use for some self-help also. Congrats on not smoking. That will help a lot, especially later.

Upper airway?: There are many possibilities which include panic attack and vocal cord dysfunction ( in which one has problem getting enough air and not out as in asthma), the latter often co-exist with asthma . If your lung function has been relatively normal and you have trouble talking when these attacks, ask an ENT doc to look at your throat. Irritants such as tobacco can trigger vcd too.

Stay quit: It is better that you continue to be off from cigarette. You could have mild asthma flares that give you the symptoms of short of breath. Other things like viral infection, anxiety etc could possibly contribute to your problem as well. You need to d/w your doctor and get checked. Don't go back to cigarette anymore. You don't want to hurt your self by damaging your lung permanently.