I've had breast augmentation of 360cc 9 days ago. Why is my left breast sore when i breath?

It sounds normal to me at this point. One breast always seems to hurt more, have more bruising, or take longer to heal. This is common.The pectoralis muscle is the muscle that is involved with the operation. Pain in this muscle usually causes pain and tenderness. Hurting with deep breaths is also common.You should try Motrin or another anti-inflammatory medicine at this point. You should also expect gradually improvement. For example, it should gradually get better not worse.I expect all is fine. See your doctor for follow up this week.Rest assured its probably normal.Good Luck.Dr Chris Saunders

At nine days post breast augmentation, it is very early and things will be tight.  Give it time to settle down. This may take a few months.