Is it true that once you're diagnosed with entamoeba coli,it will be in your system forever?

No: There is effective treatment for this amoeba and you can be clear of it. However if you are still in the environment where you caught it you could get it again.

Fad diagnosis: These little creatures are common and most mainstream physicians believe they do no harm to normal folks. Recently some "natural healing" folks have been promoting the idea that this is a hidden cause of disease, similar to claims about "systemic candida". I'd ignore them.