Nope, Amoeba are not animals. They actually have their own kingdom called
Amoebozoa. There has been a lot of work in the last decade or so to properly classify unicellular eukaryotes. In all reality, multicellular life is the exception, not the norm.
Juv, why the hell do you think that life should strive to be multicellular? Evolution is not teleological, all that matters for evolution is that the organism can survive long enough to reproduce. Unicellular life does a great job of that. There is also a huge amount of diversity in unicellular life, if you don't believe me read
this. Or maybe you think that there is one 'perfect' form of life. This is the kind of understanding I would expect from a kid. There are an obscene number of solutions to the problem of survival. I bet you don't even know that we humans rely on unicellular organisms to survive.