The longer you take it, the more the side effects will kick in. It usually starts with the bad taste in mouth, then comes the nausea & tiredness, then the vomiting. If you're lucky you will be able to go 10 days without the vomiting starting. Tinidazole is more gentle(and more effective) so they say.
But here's a really good tip: get some metoclopramide(domperidone will do too) and take it along with it. It will *greatly* reduce the nausea and queasiness, making you feel pretty comfortable(but still tired). And it will prevent any vomiting.
It's a very harmless drug that is easy to come by. Ask your parasite..oops I mean doctor for a prescription if necessary. Good luck...