This has been a common problem this year, with a lot of plants. Sometimes, when the weather has not been as favorable as it has in the past, the flower's growth will be stunted. You need to get a bloom booster fertilizer and use as directed on the box.
The plants may not be flowering due to applying too much fertilizer, which makes them grow but not flower, or if they have been planted in a different place this season, possibly not enough sun.
My sweet alyssum will bloom if I only fertilize at the start of the blooming season. If the soil becomes too rich with nutrients, it doesn't bloom very much and certainly not into September when it can become a welcome sight in the garden.
You maybe adding too much fertilizer. Nitrogen will cause the plant to produce more leaf and less flower. Remove any dead plant material such as older stems or withered flowers to make room for new ones. This plant likes a lot of sun and is weedy in some climates.
More than likely you just need to pick up some good fertilizer for blooming plants. You can get spray or granule form from Miracle Grow. Check your plant over and make sure that there are not any insect problems going on. Make sure the area around the roots are weeded as they can strangle your plant and impede growth.