i take acidophilus, by SOLGAR. i find it in the refridgerated section of Whole Foods. the kind i take is "advanced multi-billion dophilus". i took about two weeks for me to see a difference, i now take about two to three a day.
i think i can answer your third question, i had bacteria overgrowth--but taking acidophilus actually helps. i needed an antibiotic to kill the bad bacteria and acidophilus to replenish the good stuff... (the anti biotic is called xiafaxan)
my diarrhea stayed the same when i started taking it... i don't remember it getting worse, just staying constant. then i started to notice i got less attacks...(but i also started on the xiafaxan--if you suspect bacterial overgrowth there is a test for it, hydrogen breath test, or lactulose breath test)
i take it pretty much everyday (probiotics), i have forgotten a few times... i also try to eat yogurt every day--but sometimes you just aren't in the mood!
just make sure you get a good brand of probiotics. don't skimp on your health--even though it is tempting. for instance acidophilus should be refridgerated...
take care and best of luck,
what would you attempt to do if you knew you could not fail?