Are you using cartomizers = cartos where each flavor is separate, or atomizer + cart?
Are you smelling the vapor? Your tongue can only taste sweet, salty, bitter, sour and umami (MSG). Did you buy any juices that should have any of those flavors? For example, a cherry ejuice should taste a bit sweet and sour and smell like cherry (food works the same way, as do cigarettes but cigs dump their smell all over you so you don't have to remember to smell the smoke)
Are you buying decent juices?
Are you buying juices with plenty of PG so the flavor and TH comes through, or high VG juices (VG dulls flavor and TH)?
Are you using a decent ecig or something under 100mm?
Are you drinking plenty of fluids to stay hydrated? Cold water can help refresh your palate.
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Some things that cause reduced flavor and aroma - not cleaning your atomizers or replacing cartomizers often enough, wind or fan blowing the vapor away before you can smell it, not remembering to smell it, stuffed nose, sore tongue from using medium or high nic in 100% PG (I recommend high PG blends like 80PG/20VG), alcohol, drinking hot liquids, having food or drink tastes in your mouth or other aromas in the air, vaping the same flavor over and over