My Mother Has Been Taking The Drug Biosoprolol For A

My mother has been taking the drug Biosoprolol for a while now. She is experiencing severe signs of MANY OF the side effects of this drug. The headaches, dizziness when getting up from even a sitting position cold sweats, blurred vision are all getting quite worse. She also has quite severe pain in her body especially her legs. But her GP repeatedly says there is nothing wrong with her. I believe it is the drug...what should I do to help her? How can I help her..2years ago she was fitted with a ICD as she has cardiomyopathy but her breathing and general condition has only got worse.