MIZMAC
According to the medical textbook, Medical Parasitology, the drug for giardia is Metronidazole or Quinacrine.
Go to an infectious disease specialist. This is a fairly common infection so a good doctor should be experienced in this.
After you use the drugs, you may want to try the GAPS diet to repair the damage to the intestine. Be good to yourself and rest. Be gentle to your damaged intestines.