One week post ankle sprain. swelling pain and bruises still there. new symptom is burning sensation. is this normal? what causes this?

Likely normal : It can take a few weeks before the swelling and bruising subside. The burning sensation is likely from local nerves being under pressure from the excess blood and swelling in and around the ankle joint. This should also subside as the other symptoms do. If the burning sensation, swelling, bruising are worsening, would suggest seeing your doctor.

Burning: If sprain is bad enough you could have nerve injury as well. Dr. Can perform simple test to check for this looking for tinnels sign. May need nerve conduction study ...

Get evaluated: Symptoms of nerve damage can range from a numbness and tingling sensation, possibly a burning sensation, to an uncomfortable painful sensation of the extremities. For some, these symptoms are mild, while for others, they can be severe and disabling. Neuropathy can develop as a result of a pinched nerve, trauma, drug side effect, and some diseases such as diabetes. See your physician.