I personally would get a second opinion. Not because of any reason to distrust the doctor's suggestion, but because treating osteoporosis may require pre-thinking a long-term strategy over a number of years. And that means paying attention to which drugs, if taken, might make other good drugs not possible or work less well.

Fosamax, a biophosphate, doesn't preclude other possibly-better drugs later. But there are some newer drugs that work better if taken first. So treating osteoporosis is an evolving field as newer drugs have become available and a doctor with a specialty in treating it is most likely to know all of the options. Including when or if the somewhat-controversial estrogen therapy could help. (Being thin is associated with a lower general level of estrogen and possibly an earlier-than-average loss of the so-called estrogen-shield that protects bones.)

Or you could start on the Fosamax while looking for a second-opinion specialist. I just think, with those numbers, you might want an overall plan of action for comfort while you research other non-medical things you can do in addition to drugs. That way you'll know you're using all the tools currently available to address this and maybe reverse some of the numbers as well.

@mj20 with scores like that, I would think you would qualify for bone-building drugs like Forteo, Tymlos and Evenity. Evenity builds bones very fast but cannot be followed by Forteo or Tymlos.

I chose Tymlos and will follow with Evenity if results aren't good enough. I also chose Tymlos because the delivery pen has 8 "clicks" and I could start at a low dose of two clicks and move up as my body adjusted. This minimized side effects.

With a spine score of -4.7 I would start with a bone-builder not an anti-resporptive like Fosamax. You need something stronger, I think. And I also would not do weight-bearing exercises, or I would be very careful with them. Seek advice on that. I do tai chi instead!

As @callalloo indicated, there are studies that indicate the bone-building drugs work better if you have not taken the anti-resorptives (Fosamax and other biphosphonates, or Prolia).