If they did an endoscopy (put the scope down your throat), then yes, they would have found any ulcers if you had them. No, gall bladders never show up in blood work; the only sure way to find them is a hida scan (and they're not 100% accurate--I had to have three before they found out that my gall bladder was bad).
You might have a lot in common, though, with Sarita. She has unexplained D and intermitant fevers and severe pains after getting two or three bouts of parasites while in the Peace Corps in various parts of the world. She never shows up as having a parasite, but they can't explain her problem either--not even the Mayo clinic could figure her out. I've heard that parasites, even when you have them, are hard to find, so if you've only been checked once, you may want to get checked for them again.
If your vomit or poops are ever yellow or green in color, though, that's a pretty big sign that you are probably having a gall bladder problem.