a bleb is like a small balloon in your Lung. It can be caused by Emphysemas. Tuberculosis, or it could be congenital. It becomes a problem if it bursts, otherwise its just there. The treatment is to surgically remove it or collapse it. Right now the thing to do is just watch it as your Doctor suggested.
Hope this answers your question
Don't be alarmed or concerned, but be aware that its there. The studies about Pot and pulmonary disease are controversial. I would recommend that you quit smoking altogether, all kind of smoking. See the pulmonary specialist but I feel they are just going to suggest waiting. Emphysema could be the reason for the bleb, but not everybody gets them. It seems your Doctor is on top of things, maintain your relationship with him and follow general good health advice.
I hope everything works out well for you