It is possible to be allergic to marijuana - and nearly any other substance, as well. Though rare, the symptoms are in line with what you are experiencing. It is best to be honest with your doctor and tell him what you believe is causing the symptoms. Since yours appears to be a mild case (many allergic people can't even be NEAR the stuff, let alone smoke it without going to the hospital), it's likely that there are treatment options which will allow to you at least enjoy smoking once in a while.