Stromal fibrosis grew much larger:

Hello, I felt a small oval like mass below the nipple that did not hurt. I got an ultrasound, and then a core biopsy which confirmed stromal fibrosis. They said not to worry and would do another precautionary ultrasound checkup in 6 months. It has been 3.5 months since this diagnosis and the mass has gown much much larger.. it is less round, more bumpy, more flat, and very very awkwardly shaped. I would say it is 8 times larger...Is it normal for stromal fibrosis to grow larger and should I be concerned and go in earlier than recommended? Could it be something else? I am 21 years old, female, and no family history of breast cancer, but family history of other cancers.