I am praying your mammogram is a negative result.

As for the pain and swelling, I had 20 radiation treatments after a partial mastectomy. About 10 months later, I was having tenderness and terrible pain & aching in that breast, the ribs just below the breast and under the arm, as well as new reduced range of motion in that arm after almost a year of healing from radiation. CT scan & mammo were clear. My surgeon said I had radiation-induced fibrosis. It’s when muscles, tendons, ligaments & skin get damaged and hardens, basically creating scarred tissue as a result of radiation therapy. It causes range of motion issues, pain, tightness, and sometimes skin changes. We tried Meloxicam and it didn’t help much and I didn’t like more potential medications & their issues as well. I was on this site when someone mentioned ‘swell spots’. They are a form of compression padding that gently puts pressure on the fibrosis spot and begins to break it up so it isn’t pulling & tightening that area, which is what is causing the pain, etc. I found some on Amazon, but wasn’t sure which size I needed, so I found a nurse’s blog who suggested a home remedy. I tried that and it worked perfectly!!! I wore my standard compression bra from the early days after surgery (Prairie Wear brand is what I have, zippers in the front) every time I was home until the pain went away (now I wear it a couple nights a week) I put a folded up men’s athletic sock, a thick one, like 3-4 inches when it’s folded in it at the side of my breast where my tumor was removed. It doesn’t hurt at all, the sock flattens a bit. It’s just gentle constant pressure and it breaks up/stretches the area and relieves the pain. I have since found that a ‘knitted swim knocker’ works easier. It has thick stuffing than a regular knitted knocker & gives perfect pressure. I got mine from my nurse navigator, but their website is http://www.knittedknockers.org. If it turns out that is your issue, these saved my life!
I also use their regular knitted knockers everyday in my bras. They breathe, washable and have no weight to them like normal prosthetics. You can adjust the filling inside to fit you. Fabulous invention and all made by volunteers and they are free to order.