I would try some different flavors, and you've gotten some good suggestions. With that said, I don't think I'd ask for "double" flavor, that actually might taste worse than what you have... Commercial flavorings can be up to 20% flavoring, and doubling that would probably result in an anemic, poor tasting vape.
PG is a flavor carrier, so it might help to raise your PG level (it will probably increase throat hit, though).
You might look for vendors using Flavor Art flavors in their juices, they tend to be stronger than some of the other makers, so you might have some luck there.
Best of luck,
:Anna