Does amebiasis usually cause many symptoms?

Yes. Diarrhea of >1 week duration, abdominal pain and tenderness, weight loss, cramps, infrequently fever. There is usually history of travel to an endemic area beforehand.
Most often not. Amebiasis causes illness in 10- 20% of those infected. It can lead to loose stool, cramps ; abdominal pain. Severe form (dysentery) can lead to fever ; bloody diarrhea. In rare cases it has seeded other parts of the body such as the brain or liver (where it can form an abscess).
Yes. Of course diarrhea, blood in stools, can also lead to severe complications need investigations both blood and stools and treatment.