Yes reinfection can be a big cause depending on where you live and your circumstances. Also, Giardia can sometimes get sequestered in the gall bladder or pancreatic ducts and they can do a scan to find out. For the treatment you may be able to ask your doctor if there is a compounding pharmacy that can make Quinacrine as this sometimes is an alternative. Also, ask your doctor if Furazolidone is in the same group as Metrodidazole to see if you would be allergic to it or the Qunacrine. If not maybe one of these drugs may be an alternative. Also, another thing they can do is prolong or up the dose of the drug you are using. These are all things to think about. Buy bottled water and cook with it and also boil anything that is suspect.
mkh9
Can I ask you if you have had any water tested where you live? I am wondering if you are still infected because you are being reinfected. Do you have well water?