Things it could be:
Tbf there are plenty of other possible causes of non-cancerous breast lumps (AKA benign lumps). The most common being cysts, blocked milk-ducts, fibroadenomas, fat necrosis, and sclerosing adenosis.
Here is some helpful information I found online about benign lumps:
How cysts are diagnosed and treated: Your healthcare provider may find a cyst during a physical exam. He or she may confirm the diagnosis with a mammogram or ultrasound. You may also have a fine-needle aspiration. This involves guiding a very fine needle into the cyst and drawing fluid from it (aspiration). This also serves as the treatment for this condition. Once the fluid is aspirated, the cyst collapses and disappears. But, cysts can reappear later, in which case they are simply drained again. Cysts are seldom cancerous (malignant).
How fibroadenomas are diagnosed and treated: Your healthcare provider may diagnose this type of lump simply by feeling it. But, he or she will want to confirm the diagnosis with a mammogram or ultrasound and fine-needle aspiration. Sometimes, in very young women, the fibroadenoma is not removed. However, since sometimes these tumors enlarge with pregnancy and breastfeeding, your provider may suggest having it surgically removed. While most fibroadenomas do not lead to cancer, there is a type of fibroadenoma that has been linked to an increased risk of cancer, particularly in women with a family history of the disease.