Cantaloupe Blooms But Fruit Dying?

This is my first time. I have 1 cantaloupe plant that had grown 3 small cantaloupes where only 1 survived. It is now 2" in diameter. There are lots of flowers, but the fruit beside it is dead. I had some powdery fungus that I have been treating, but it has not infected the entire plant. A friend told that fruit flies are killing the tiny fruit. The same thing is happening to my tiny zucchini fruit. Do you know what is killing it and how to stop it?