There are too many cysts in my breast.

I had a breast ultrasound, and there were too many cysts..ㅜㅜ The doctor said I need to have another ultrasound in six months. They said I need to continue follow-up examinations. If the cysts grow larger, it might be bad.. There are more than 10 cysts in both breasts.. Why do so many cysts form like this? I'm worried about having to be tested again in six months..