Asthmatic, Ordered Symbicort, Feel Uneasiness On Its Intake. Reason?

I am an asthma patient and have recently ordered symbicort from a mail order pharmacy. I received three canisters. After about a week with the first canister I was feeling very short of breath, tired and clammy, and had difficulty preforming my normal exercise...just as I did before being diagnosed with asthma about 6 years ago. I thought maybe there was a problem with the canister I was using, since it felt as though I was completely unmedicated, so I opened another. Within a day or so I began to feel much better and was able to go about my regular exercise without difficulty. That lasted about a week and I am once again beginning to have difficulty. My question is whether it is possible that I have received defective canisters, or are they manufactured in a way that would make that virtually impossible?