Have been taking Zocor for about 5 years now, leg and knee pain ...

Have been taking Zocor for about 5 years now, leg and knee pain makes in almost impossible for me to walk. Has this medicine caused permanent damage to my muscles and joints? a question I would like to have answered. I am 71 years old and up to now could walk endlessly without pain or distress. A couple of years ago switched to generic Zocor which is SIMVASTATIN. Noticed no difference, but still have difficulty walking very far and am from side to side unstable, when I walk, because of pain in one leg or the other. Now what is the answer, has this medicine caused permanent injury, it has caused me to be more comfortable sitting and have things to do. Will the pain go away and will I regain my strength back in my legs? Wonder what is the answer. Tom.