Remedy For Muscle Tightness In The Center Of Seat On One Side Leading To Sciatic Nerve Pinch

I m a male 70 yr. old. I have had 2 hip replacements. 10 & 12 yr. ago. Both work well. However, I have muscle tightness in the center of my seat on one side. It gets so bad that the sciatic (sic) nerve get pinched and causes my foot to get numb after walking a few minutes on hard surfaces. Stretching the ham stings provides temporary relief. Is there a good stretch or some other activity to remedy this problem