I am experiencing a slight enlargement of one breast. It used to be smaller than the other and now it is about the same size. There are no lumps in the breast or under the arm. The muscle that connects from the breast to the armpit/arm is kind of sore but only if I feel for it and then my upper under arm on the arm feels like it is warm but I could be imagining this . I am 46 and probably perimenopausal. I just finished having my period for this month. I have had some back pain. I also am experiencing some chest wall tenderness deep under the bottom of my breast. Is this anything to worry about. Could it just be back pain or muscle strain that is radiating to the breast? The breast is still that same color as the other one and to look at it there is no difference from the other one. There is also no difference in the way one breast feels to the touch from the other. I just feel that there is some very slight swelling.or fullness. Is this just a perimenopausal symptom? Or should I be worried about cancer?