Pain Knees. Had One Replacement On Right Knee, Left Has

Pain knees. Had one replacement on right knee, left has hurt for years, past month right knee hurt so bad, I could hardly get around. Went to Doctor, they said it was due to putting all weight on replaced knee, on scale of 1-10, pain was 8. I have always prided myself of handling pain. I am 73 and over weight. Several times Dr. Has told me to loose weight. Have tried, but it is so difficult to even walk. What can I do for help.