I can't poop because of my OCD

It sounds funny said like that, but it's anything but. I have housemates and whenever I have to do something more than just pee, I keep thinking that they'll hear me. I can't relax enough to get it over with. So much that I've even had health issues because of this, and it's taking a toll on me. I always hold it in until I can't anymore because at that moment, my body trumps my mind, but it can take days at worst.

I know that it's just a natural bodily function, but my OCD doesn't care, of course. I try to go when they're not home, but I can't always choose the time. They also have day-offs on top of weekends.

Has anyone else experienced this? How can I win against this?