Hello Nancy,
Their could be a few reasons. First is inefficient pollination. Tomato plants are self pollinating, but they still need cross pollination from the other flowers on the plant to pollinate. Some people just shake the plant a few times a day to stir up the pollen, some people use an electric tooth brush on the back of the flowers to shake the pollen loose. but I think the best and easiest way is just use one or two oscillating fans. The other reason may be stress from temperature, humidity, too much Nitrogen, and/or low light. I'm guessing your
cfl light source is insufficient as well.