Hello,
It can be due to bruise due to trauma skin. The blood under the skin which causes the discoloration of bruising should be totally reabsorbed by the body in three weeks or less. Apply warm compresses and take some anti inflammatory pain killers.
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.
I ment to put brown spots on my arm