ah yes, the dreaded Olfactory Fatigue Syndrome. It hits all of us eventually. What you basically need to do is get your nose to sense and get used to some radically different aroma than your liquids. Yes, changing up from a tobacco to a fruit flavor can help, or adding a bit of sweetness like sucralose if you vape unsweetened, or even a hit of cinnamon or menthol can do the trick. Unless you vape a lot of coffee or chocolate flavors, here's a trick that professional tasters (like for wine/whiskey, tea, and yes even perfume makers since it's about your nose not your tongue) use: they inhale strongly in a container that has strong coffee grounds in it. This has been a trick used for centuries to reset their olfactory sense. I do it sometimes when changing flavors doesn't work. cheers mate.