From “The Joys of Yiddish” by Leo Rosten:
To help you distinguish kvitch from kvetch from krechtz (a salubrious set of niceties) I offer these observations:
You can kvitch sedately, charmingly, out of happiness; to kvetch is always negative, bilious, complaining; and to krechtz is to utter grating noises of physical discomfort or spiritual woe.
Kvitching may be hard on the ears, but kvetching is hard on the nerves. As for krechtzing, it should be reserved for a hospital room.
Some families produce personality types who are adept, even effusive, in their kvitching; other families specialize in kvetching — communal grousings drenched in self-pity; and some krechtz so loudly and so often that they sound like a convention of hypochondriacs.
If you take the trouble to familiarize yourself with the nuances of kvitching, kvetching, and krechtzing, you may zestfully add them to your arsenal of exclamatory locutions. Connoisseurs should enlist them for the relief of English words that are becoming exhausted from overwork.