Hi,
Welcome to the ehealthforum and I am glad to help you out. Your concern is regarding the low back ache. This seems unrelated to the miscarriage that you had unless and until it was a D+C. D+C can introduce infections in the vagina which may cause pelvic inflammatory disease. It can also be accompanied by adhesion formation which may cause abdominal and back pain.
Other common causes of back pain are strain of muscles or sprain of ligaments. But there are number of other causes also like damage or injury to spinal nerves, bones, or discs. For treatment of acute back pain, take adequate rest. However ,if you need to continue working then consider using a brace or corset for a few days. You can also take over the counter non-steroidal anti-inflammatory drugs. If the back pain worsens or persists then please get it evaluated from a gynecologist and physician.
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.