I Was On Fosamax For 7 Years And My Dr

I was on fosamax for 7 years and my dr took me off of it. I was still osteopenic. I have not been on fosamax for years. But, my bone density reports did eventually show no osteopenia. I have walked and been faithful to exerciseand healthy eating.
?why did I have to go off of it and and can I return to taking fosamax after so much time if I have a bone density report later (in a few years) showing osteopenia?