The most common reason for tomatoes not setting fruit after they flower is hot weather. Anything above 90 degrees is too hot for fruit set but you may be able to add more shade to your plants and trick them into fruiting before the really hot weather arrives. There are many creative ways to provide shade during the hottest time of day but your local garden club or Master Gardening  group will have the best advice on growing in your unique region. There are several different climate zones in Arizona so the specific dates of when it is best to grow tomatoes will be different depending on where you live. Your local experts will be the best source of specific advice to beat the heat. Keep growing, Marianne Binetti