I have that sort of problem from time to time. Something they call fissures and a tag. A tag is somewhat like a hemmorhoid, it's just basically excess tissue that has been pushed out from the inside and hangs there, annoyingly. I had one surgically removed when I was 18. I have one growing back now, and may remove it, but not until it's necessary. Mind you, I finally removed the first because it got to be about as big as a quarter... and because it was sensitive tissue, it was easily sore. And really obnoxious.
The fissures are best explained in a really gross kind of way. You know how in the winter you get chapped lips and they're so chapped that they split? Same idea, only with the butthole area. Because of the excess wiping, my butthole gets chapped, and I get fissures which are the butt's equivalent to cracked lips. (I apologize for this, I realize none of you want to hear about my butthole... lol).
Anyway, I've had similar issues. And whether from the fissures or the tag, I've bled in the toilet many times. Enough to make the water pink, same as you said. Once or twice, it was enough to make the water sufficiently red. I just ignore it, and it goes away. *shrug* Sorry I've been of no help, but you're most certainly not alone.