Giardia are microscopic and cannot by seen by the naked eye. You will not see any killed by the flagyl.
You can get more information on Giardia and its symptoms by just doing a Google search and that may answer some of your questions.
It is difficult to actually test positive for Giardia, they are hard to find in a stool sample. You may have just been diagnosed by symptoms.
You may indeed have other parasite issues and hopefully someone more knowledgable will chime in on that issue.
In 10 days I would have liked to see an improvement if Giardia is your main problem. I know it takes time to cure oneself of it, but a little improvement would be nice. Have you noticed anything better?