Are you sure your doctor is asking you to now take a bisphosphonate? Because I don't think that's considered a bone-building drug. It's the same drug as Fosamax (and Reclast), which you said you already tried but had GERD issues when taking it. Bisphosphonates work by slowing down bone-break down, which also slows down the bone building process. They are supposed to maintain your BMD because you are retaining old bone.

I believe bone building drugs are those such as Forteo, Tymlos and Evenity. But once you quit taking them, you will have to take a bisphosphonate of some kind (Fosamax or Reclast) to keep any BMD gains you made.

Ask your doctor the specific name of the drug they want to prescribe. Then, remember that bones change very slowly so tell your doctor you want to take time to investigate the drugs available before you make any decisions.

Also, as mentioned by another person here, it would be helpful to know your DEXA scores and your age.