Why is there pain in left breast a year after Breast Augmentation?

In all likelihood it is a muscle strain or pull. However, this is an online diagnosis which is notoriously inaccurate. Discuss your compalints with your plastic surgeon and be examined before dismissing this.

If you are one year after breast augmentation and have pain it could be many things, and it is best to get an exam by your surgeon.

This is probably due to the capsule.Remember,everyone gets a capsule and sometimes there will be pain as the capsule is stretched from your period or perhaps a little mastitis or breast inflammation.Little sensory nerves get bound down in the capsule so any stretching or pulling can cause a little discomfort.

Pains that come and go with breast augmentation are usually related to simple trauma. However, a persistent pain may indicate capsular contracture. Capsular contracture can occur at anytime after breast augmentation and is the phenomenon where the scar tissue surrounding the implant begins to tighten, thicken, and distort the implant. This can be associated with pain. Many other issues may cause pain such as swelling during your period, cysts in the breast, or lesions in the breast. I recommend a followup with your plastic surgeon, breast surgeon, or primary physician, particularly if the pain continues.

Usually when the breast starts to hurt so long after augmentation,  it is usually related to the development of capsular contracture. Just because you have implants doesn't mean that every symptom is related to them. You may have just had enough of a trauma with your horseplay, or you might have an inflammation in the breast itself. If it doesn't get better on its own (maybe with some icing) in a week or two, then you should have it checked out by either your primary care doctor, your plastic surgeon or a breast surgeon.