I agree with Flaming Turnip. If you feel fine and it's not inflamed any more, I don't think you have to worry, but I guess you can show the object to a dr. and see if he can figure out what it is.
I once knew a guy who had gotten a nail impaled in his rear end when he was a kid, and it went in deep and had always stayed there. Every once in a while when he sat a certain way he could feel it, but other than that, it didn't bother him. One day, a couple of decades later, the same thing happened to him as was happening to you, and then out popped the nail.
Your body just wanted to get rid of the object, and it did. Whatever it is, it's probably all good now.
I have to disagree with Aileene. Okay, don't take it to the dr., see if someone else can figure out what it is. But what if it's only three little grains of something, and now it's out? Doctors and nurses aren't superheroes, they are human beings, and every once in a while some tiny thing happens. Assuming there was only this tiny object in you, I think it's immoral to sue, frankly. S&*t happens.