Is mastectomy only way for me to get rid of painful scar tissue and cysts inside my breasts?

Possibly: But seek opinion of breast surgeon. Subcutaneous mastectomy and implants may be a choice depending on he specific anatomy.

No: There are multiple natural remedies for breast pain and cystic disease. None work in most, but all work in some (vitamin e, evening primrose oil, caffeine intake reduction, topical anti-inflammatories, etc). If these fail, low dose (10 mg per day) tamoxifen, in the right patients, works very well. See a breast specialist. Mastectomy should almost never be necessary.