Why did I pee out a rock?

I was peeing at my house and my stomach was hurting. I started to feel pain in my wiener and then it really started to hurt very bad! Then I pissed out a little pebble. At first I thought it was poop but when I picked it up it was hard. It's about the side of a nickel. Please help! The rock teared up the inside of my and now I pee blood.