From the research I've done, the protozoan doesn't get into the blood stream. Eventually it just dies off but can take anywhere from weeks-months if left untreated.
My ER copay is $100. I can't get an appointment with my PCP, they will only let me see the Nurse Practitioner who I can't stand. Furthermore, I don't think they will just write me a script for Metronidazole. Most likely they will require multiple rounds of stool samples which could take another week. This has been going on for over a week and although I'm staying hydrated, I've lost weight and cannot eat like I usually would to support muscle building.
If I thought it was as easy as going to see my doc and having him write a prescription, I would've done that. The last time I went for a sinus infection, they started asking me "standardized" questions about whether or not I was feeling depressed and if I was having suicidal thoughts...again, there for a sinus infection. The US medical industry is entirely insurance company driven and frowns upon intelligent patients who actually do the research themselves instead of blindly following the advice of a stranger with a diploma on the wall.
First, if what you said about previous doctor visits is true, my advice is to fine yourself a new primary care physician. Your doctor will have to identify the parasite before prescribing treatment. This is done from a stool sample . Some people have allergies to Metronidazole, you could be one of those folks unless you've taken it before with no adverse side effects..
Second, if time is an issue, medications ordered from online pharmacies that don't require script and ship from outside the U.S. can takes several weeks or longer to arrive. They might sit in customs for a month before being released or confiscated, in which case they will never be delivered.
Your $100 ER copay is pretty much the norm today. Insurance providers discourage folks from using the ER except in the case of an emergency. If you have insurance, it is likely you won't get treatment for a parasite there since it probably isn't considered an emergency.
If you read about Protozoa, then you know this is a general classification for a huge variety of parasites (30,000 to be exact), some are more aggressive and dangerous than others. Your decision to treat this yourself is dubious to say the least.