The unpredictable side of economics is of course the behaviour of the various economical agents, and regarding this I think economics is closer to astrology than to psychology.
Maybe sociology, since money matter because it can be exchanged between people, but personally I don't think you'd be wrong for thinking about economics as a narrow but important branch of sociology/psychology, in the same way you might think of biology as a narrow but important branch of chemistry and physics.
There isn't. There's a practice and set of local "crafts pertaining to". That's why it's econom(ics). [-ikos, -ique]
Like electronics, acoustics, politics...
As opposed to being econom(ology), a more systematic science [-logy (logos)] being a branch of knowledge.
Even hardcore economists aren't keen to raise it to the level of a "science".
-ic/ics mostly just means "pertaining to" (minus the craft bit) and like all things in the English language, is never a hard and fast rule.
Is "political science" real? (I personally think there's a case), but why did that have to arise besides politics? I studied electronics and am happy to report, compared to its foundation in physics, it's an ever changing craft of black magic and tricks you can do with silicon and electrons. Need proof? Where is the craft of thermionics today?
As for economics, I don't really know. Some days I have hope in its use. Other days I think its very conceit is the root cause of much it sets out to solve.
Both are made up in the sense that the algorithm itself can be modified by regulation or social convention. There's even a field of economics dedicated to finding out how to engineer such an algorithm (a mechanism) to satisfy a given objective.
But if the algorithm is more or less stable, then it makes more sense to study it rather than just parts of its state. That's the difference.