What ecig are you using? Some people have problems getting good flavor from tanks. If you are using any kind of atomizer, I had to alternate attys weekly and clean the used one to get the flavor back. Some instead rinse the atty they are using nightly. I now use cartomizers.
The more nic, the less the flavor will shine through. If your ecig isn't strong enough for you, consider buying a better ecig.
The more VG, the more flavor will be dulled.
If you keep vaping the same flavor over and over and over, you will be used to it and not taste it. I vape 2 contrasting flavors in cartomizers so they are totally separate.
If you don't smell the vapor, then you will miss much of the flavor. The human tongue can only taste sweet, salty, bitter, sour and umami (MSG). If a fan or wind prevents you from smelling the vapor, try exhaling through your nose. Ditto if other aromas around you prevent you from smelling the vapor.
If you are using high nic your tongue (or mouth, throat, lungs) can get sore and numb and that can dull flavors.
Different juices and even juices within the same vendor have differing amounts of flavor. Some people like light flavor for all day vapes. Some like stronger flavor. Try other juices.
other things that can kill flavor - stuffed nose, food or drink flavors in your mouth. alcohol drinks, hot drinks, dirty atomizers or singed cartomizers
Remember to drink plenty of fluids - vaping can be drying. A drink of ice water can help refresh my palate.
As I said above - I vape 2 contrasting flavors in cartomizers so they are totally separate. Each refreshes my palate to taste the other. That is what worked for me to not get used to a flavor.