Glad to know that your biopsy resulted in benign findings.Congratulations!
It's not unusual to feel breast discomfort after a biopsy.Many factors will effect the individual experience such as type of biopsy, location etc.. During this procedure,nerves are often irritated and it can take a few weeks to heal but it should eventually improve along that time line.
Try not to stretch your arm too much..I guess the stretch line down the incision site could also be due to the biopsy,depending on how much tissue was removed .But if you are concerned about it,call your doctor for reassurance.
To ease the discomfort in your breast,apply some warm compresses, gently massage your breast, wear a good supportive bra and try not to lift heavy things.You could also take some OTC pain killers,like Acetaminophen or ibuprofen that usually can address the pain related to this type of nerve injury. .
Best wishes and hoping that you'll feel much better soon...