hmbrglr,
you could try Reclast to avoid the reflux. I'm glad you are off Prolia with only two injections.
Call your physicians office right away. Meanwhile, don't think about stopping Fosamax before replacing it with another bisphosphonate. Be careful about the instructions for taking Fosamax. Remain upright and don't take your exercise until several hours after ingestion.
Put the rush on your medical office.

Are you seeing an endocrinologist or rheumatologist? The medications you’ve mentioned will only slow down bone loss but will not necessarily increase your bone density. Fosamax can shift the bone metabolism away from bone resorption by killing off the cells that break down bone (osteoclasts) but because bone formation relies heavily on signaling from bone breakdown, it eventually stops while on Fosamax.

Our bones need to be replaced over time as we use them. Normal bone metabolism includes bone replacement. Without it, our bones develop microfractures and lose their strength.

Specialists may consider using another class of drugs called anabolics which help build new bone. This would be the drugs Tymlos (Abaloparatide) or Forteo (Teriparatide).

I was on Fosamax for over five years. I didn’t have any GI side effects like you are having but I did fracture my T8 vertebra on it. I had no idea that bone remodeling stopped or was severely suppressed on this drug.

I am now on Teriparatide in the hopes of finally starting the bone remodeling and formation process again after many years.

Can you perhaps see a specialist to discuss your long term treatment? Many of us just get put on a drug using short term thinking when I believe we need a long term plan for the rest of our lives.