Words to replace swear words?

I have found myself feeling the need to swear a lot lately, I'm just really overall unhappy. I don't want to hear anything such as "fudge", weird sounding made up words or anything of that sort.. I don't want anything immature sounding. I like keeping my vocabulary fairly ... mature? Although I have exceptions when I'm in a playful mood. I don't even know if there would be anything that didn't sound informal... but if you could help, thank you.