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Wiktionary
what's eating you

interj. (context idiomatic English) What is annoying or bothering you?

Wikipedia
What's Eating You

What's Eating You is an American reality documentary series about people with eating disorders. The series premiered on October 13, 2010, on the E! cable network.

Usage examples of "what's eating you".

Now, you can stay up all night while I go get some sleep, or you can spill what's eating you.