eat away at

Etymology
From.

Verb

 * 1)  To erode.
 * The river is eating away at the river bank.
 * 1)  To consume or use up, erode or wear away gradually.
 * The expenses ate away at our profits.
 * 1)  To cause to feel uneasy, troubled, worried, guilty, or vexed; to bother about something.
 * Not confessing that I had stolen the money ate away at me until I could no longer sleep.