gnawing
From Longman Dictionary of Contemporary Englishgnawinggnaw‧ing /ˈnɔːɪŋ $ ˈnɒː-/ adjective [only before noun] HURT/CAUSE PAINWORRIEDworrying or painful, especially for a long time gnawing doubtsExamples from the Corpusgnawing• What all clients have in common is a gnawing desire to make a quick profit, and a likely fatal gambling instinct.• a gnawing dissatisfaction with day-to-day life• It was not an obsession then, only a gnawing doubt.