I had the same problem. My tom plants thrived, plenty of blossoms but no fruit so I brought in a fan and an electric toothbrush to help pollination. I have an inside tank so I needed to help pollination and light.. The plant took up all my room so I ended up pulling the plant and replacing it with cukes so we'll see what happens. The other thing is your grow lights. I was told by a gentleman who teaches hydroponics that it takes a really good growlight to produce fruit... and it turns out that the one he uses costs like $ 600. plus. So I'm perfectly content in growing my greens if that's all I can grow. I was also told that toms are very heavy feeders. If they are outside, I don't know .
An over-abundance of nitrates can cause your tomatoes to put more energy into growing the plant itself, rather than producing fruit. Now that your nitrates have dropped off, you might start to see fruit forming. Make sure the flowers are being disturbed so they pollinate, either by hand, or by circulating the air with a fan.