Hi and welcome to the forum! I am happy that I can help you.
You like to know whether you may have a lung cancer.
Lung cancer usually appears when people smoke for rather a long period of time, such as ten to twenty years. The time when the cancer appears depends on the amount of cigarettes smoked per day. People who smoke less that ten cigarettes per day are less at risk to develop lung cancer. However, smoking is the reason why smoker may experience breathing problems, such as often infection like bronchitis, worsening of the symptoms of underlaying asthma and etc.
Lung cancer may be presented with persistent cough or difficulties caused by the pressure of the cancer over the other organs, such as esophagus, nerves, veins and etc. Asthma and bronchitis may sometimes be presented with chest pain.
Given the symptom that you described, chest pain, it isn't likely that you may experience lung cancer. The difficulties that you feel may be caused by the asthma you already been diagnosed with. You may consider seeing your doctor for further advice and treatment options. Also you may consider quiting smoking not only marijuana but tobacco as well.
Please keep in mind that provide with medical information here only. I am not able to diagnose medical conditions online. Please contact your doctor for further advice, diagnosis and treatment options.