I am 28 years old. I have had my period for 16 days straight and it has been light some days and heavy. Now I am on my 16th day and my body is in pain. I am not pregnant, I am 100 % sure. What can I do to make this stop, I honestly don't know what to do. Please any advice.

You need to go to your doctor. Bleeding this long could be a sign of low iron (anemia), or a number of other problems.