What do you feed your tomatoes, Molly?
I grow them straight in compost. I just have comical bad luck with growing things. The first year they got some sort of bug/disease that acted like squash vine borers. They just fell over dead one day. I had some animal eat all my seedlings last year. And this year the temperature has been too hot most of the summer for anything but cherry tomatoes.
Depending on what compost you use, your plants might not get enough of the nutrients they need to fruit and flower. Two major factors play a role in that part of plant production: time spent in light and amounts of P and K that is absorbed by the plant.
Fruiting and flowering plants need 12 hours of light 12 hours of rest. They also need lots of Phosphorous and Potassium to trigger the fruit and flower stage. In addition to the P and K tomatoes also need calcium and magnesium to prevent diseases like blossom end rot. I know many gardeners advocate for compost only feeding, but if you think about it people don't like to eat just one kind of food. Plants don't like to eat one kind of compost as well. Change your plants food and see if that helps. Gardening is science with a dash of luck not the other way around.