Is there a word for getting excited about nothing? [duplicate]

I think Shakespeare's Much Ado About Nothing is quite relevant. In more contemporary English "a lot of fuss [over/about] nothing" means the same thing.

I have heard people speak of "making a molehill out of a mountain" (an inversion of the more common "making a mountain out of a molehill").

I'm not certain it meets OP's exact definition, but a storm in a teacup* might fit. It's usually used where the fuss is over some undesirable thing, rather than a trivial but (slightly) desired outcome.

Another possibility is don't sweat the small stuff (used to tell people not to worry about trivial or unimportant issues). It can be used as don't expend too much effort [to achieve some trivial gain], but it's normally advising what not to do, rather than a description of what you did for little gain.

There's always this graffiti, commonly found on the walls of UK public toilets...

Here I sit broken hearted,
Paid a penny and only farted

In practice, I think the most common phrasing is just a lot of effort for little reward, but in my particular neck of the woods I often hear life's too short to stuff a mushroom.

*As I've just discovered, the American version of this is very definitely tempest in a teapot.

Perhaps Shakespeare's oft quoted line from Macbeth

. . .it is a tale told by an idiot, full of sound and fury, signifying nothing.

The full quote is an even more dramatic commentary on an entire life being lived to little outcome

Out, out, brief candle! Life's but a walking shadow, a poor player that struts and frets his hour upon the stage and then is heard no more: it is a tale told by an idiot, full of sound and fury, signifying nothing."