Sami, I doubt that anyone could say for sure what's causing the diarrhea. I just know that mine started when I started PPIs over a year ago and ended when I quit. Like you, I had trouble with splitting nails as well as hair loss. If you Google the name of your PPI and side effects, you'll find a list of possible effects as long as your arm -- some minor, some very scary.
On what basis did your doctor decide you needed PPIs? Did you have an endoscopy or other test? Have you had a colonoscopy? Test for H pylori? My doctor prescribed Prevacid after a three-minute description of my symptoms. It seems to me doctors should at least advise a milder form of medication before bringing out the neutron bomb.
You asked what I'm taking. No drugs at the moment, but I'm watching my diet very carefully -- no sugar in any form, no coffee, no high-carb foods. Also digestive enzymes at mealtime, and ginger juice every morning.
As you know, anxiety makes HB/reflux worse (maybe causes it??), so do what you can to set your mind at ease. Hope you're feeling better soon.