Answer: There are a couple of possibilities I can think of, the first being that you may have overdone the nitrogen which can cause exactly that situation. The other is blossom drop, which happens particularly when the soil is dry and the weather is hot and windy. (Tomatoes need an evenly moist soil to do their best.) Environmental factors such as heavy rain can also interfere with fruit set. One more possibility would be some sort of nutrient deficiency, so if you haven't run any basic soil tests for a while you might consider it just to be sure.
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