continue with fosomax or try new medication?

I am a 55,soon to be 56 year old female. I no longer menstruate,haven't for 2 1/2-3 years. My first bone density test was in 2002,L1-L4 was -2.4 and femoral neck was -3.2. The doctor had me start with Fosomax once a week. Next dexa scan was 2004,L1-L4 was -1.9 and femoral neck stayed same at -3.2.  Continued Fosomax and citracal. 2006 test read -2.0 and -2.9,and now 2008 test Ll-L4 -2.3 and femoral neck is-3.1  I walk two to four miles twice a week. I am concerned about the numbers and their implications. Doctor wants to change to Evista or Forteo, would like your opinion on this and if to continue fosomax or stop.