What can one use to ease stomach upset.?

I did a quick search and it appears there are prescription probiotics so it would be worth asking your doctor. I buy the Lactobif 30 from iHerb and pay $22 for 60. I take just one a day so that's just a little over $10/month. It has 8 different strains and so far I've had no diarrhea and nausea went away after a few weeks so I am comfortable sticking with the product.

When I was on the antibiotics, I was very successful using ginger - Ginger tea, Ginger beer made with real ginger and Ginger chews or hard candies. Also, it helped to never have my stomach be completely empty - tiny meals throughout the day helped a lot. It also helped maintain my weight as I had no appetite.