Hi llene: That's great that your getting your calcium, D, and exercise to help maintain your bone density. Congrats on being diligent in this area.
You mentioned that you have brittle bones, how did your Dr determine that? Did your t-scores decline, did you have a bone biopsy, or did you sustain a fracture? If any of these are the case, I could see why your Dr might want to change your medication to something else besides Fosamax.
Reclast is a bisphosphonate, but there are differences between Fosamax, Actonel, Reclast and Boniva. You only have to look at the clinical trials on these meds to see that each differ in some way in fracture prevention, ingredients, side effects, etc.
I understand your concern about switching to Reclast, since you and your Dr feel Fosamax has weakened your bones, but you are the only one who can make this decision. Read as much as you can on this drug and see if that helps you to make a decision.
Reclast outperformed Fosamax in reducing fractures so maybe that's why your Dr wants you to try that. Below is a link that explains this from The New England Journal of Medicine-Reclast.
http://content.nejm.org/cgi/content/full/356/18/1809
Good luck deciding what to do...