hi      because of breast sagging back does not ache. there may be some other reason. for breast sagging option is uplifting of your breast by surgery called as mastopexy . breast sagging occurs due to loss of skin elasticity , genetic cause.prenancy. so in this surgery they will remove excess skin and reshape the breast . but for which you should not have any chronic illness. and if you want get pregnant u cant undergo . it may affect because breast will enlarge again . and after surgery also you have to do exercise to keep breast uplifted. so consult a plastic surgeon and discuss with them .