Urges and compulsions

Why does OCD make me want to do things I know for certain I'd regret? Really, really horrible things that would ruin my life and make me completely miserable. And yet it's like I want to do it so badly. It's a constant urge that's taking everything in me to resist. I'm so tired of it. I can't stop thinking about it. And these things aren't just kind of bad, they're seriously messed up as well. What do I do?