Flagyl (metronidazole) and Ciprofloxacin are probably the drugs he was given. These are the first in line for parasitic infections. I've been on them several times and recently went through a 2-week course of Flagyl myself.
I've got to say that some of that sounds very familiar. The nausea, increased diarrhea, fatigue, metallic taste in the mouth, etc. are all side effects of the Flagyl. It's a very potent drug, so you can expect that the side effects will be a bit rough. The nausea was the worst. The good news is, most side effects go away within five days of starting the drug. Also, it's dangerous to stop taking an antibiotic before you are finished with the entire course because the bacteria can build up a resistance to that drug if they are not all killed off. That's why it's so important to stay on it!
Tell your boyfriend to talk to his doc and let him know all the side effects he experienced and also that he quit the drug early because of them. When I took them, I counteracted the side effects with an anti-nausea drug, which helped a lot.