What you are experiencing is a loss of cranial nerve function, specifically cranial nerves VII, IX, and X. They synapse in the solitary nucleus, this synapse creates the sensation of taste. When you lose your sense of taste, is it your entire tongue or a partial distributio of your tonge (like the anterior 1/3, medial, or posterior 1/3?). Complete loss of taste sensation could be indicative of central nervous system damage and if this is the case, you need to evaluate how important smoking is to you. As you continue, you may lose taste even when sober, and develop even more serious side effects. Another differential to consider would be nasal congestion as a result of puffing. This could also lead to loss of taste sensation, and be a result of a minor allergic reaction to the marijuana smoke.