Learn English – Idiom request: Putting too much effort, but the return is so low that it was not worth the effort

This phrase is pretty old. And not in very common usage with the youth. Though I might occasionally say "I was burning the midnight oil last night", I would certainly prefer the phrase "I/We pulled and all-nighter". Note the grammar requires the use of an and all-nighter is non plural (feels weird quoting grammar usage for a slang phrase).

The origins of the phrase are not conclusive, but perhaps pertain to poetry uses meaning to need an oil lamp burning past midnight to complete work 1, or the burning of old holy oils the night before new ones are consecrated 2.

One fairly common expression is trying too hard.

For example usages, it's not too hard to find advice columns entitled something like:

8 Signs You're Trying Too Hard To Make A Relationship Work

10 Signs You’re Trying Too Hard and Turning Him Off

13 Signs You Are Trying Too Hard In A Relationship