Breast implants can cause change in weight but your back problems seem unrelated to the implants. The commonest causes of chronic low back pain are lumbar strain, nerve irritation, bone and joint conditions (arthritis), osteoporosis, lumbar radiculopathy, narrowing or stenosis of the spinal cord cavity. Even bad posture can lead to low back pain.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.