First and foremost, was this consensual? I need to make sure you aren't feeling bad for something that was forced upon you. And, was this 5 guys separately (having sex with them individually) or 5 guys at once (like an group sex situation)?
If it wasn't, you need to speak with someone (preferably police) and seek counseling. Women in this situation oftentimes feel guilty when it isn't their fault at all.
If it was consensual, I imagine you feel dirty because people don't talk about it openly. And I'm not exactly sure how frequently this act it done, but people generally don't talk about it. Maybe you want to think about if this is something you really wanted to do, and if you'll ever do it again. I've felt guilt about sexual acts I didn't necessary want to do but did consensually just because. Reflect on how you're feeling now...what made you feel this way? Is there something in particular you were uncomfortable with?
These negative feelings usually follow an act that someone is unsure about. Think about that, and then learn from it. I need to urge you to talk to someone though, especially if this was not a consensual act.
Good luck honey.
:: hugs ::