[Ginie]

You should have it inspected by a doctor, they will probbaly do ultrasound thing. It can be anything, so instead of worring what it can be - go to a doctor. When it comes to any type of tumors in a breast then it is mainly assosiated with either high prolactin or estradiol, have those two checked. Also lumps are just fibroids and you noticed it when there was more water retension than normal (this is what elevated estrogen does to the body). Talk to your doctor about it.