I have a 4 foot tall Goji Berry plant that has been prolifically producing flowers all year long. None of the flowers ever become fruit. I've witnessed hummingbirds poke into each flower because they love purple flowers more than any other color. That means they should be pollinated, right? The dozen other fruit trees in my garden have no problem pollinating naturally - I have many wasps and bumble bees.
It might be diseased. Most of the time, it has what appears like talcum powder on its leaves. I sprayed it down with neem oil once and it went away, but came back within a week. Maybe the powderiness is natural to its leaves???