I Have Been Told I Have Crumbling Bones,am Waiting For

I have been told I have crumbling bones,am waiting for MRI scan.i have always exercised,and worked all my life,now I am 66 and retired,but have been doing Aqua aerobics and swimmin,I used to ride my bike ,but now walk instead.what is causing this,also cannot straighten my fingers to use a fork ,and cannot lift my arm (both on my left side).my doctor said what I have is rare,can you help ..