This happened to my pup shortly after I got him, and he had to have an enema
but it helped and he's done fine since. I wouldn't wait too long because it can be really bad for them. Also the pink flap you're talking about is a prolapse (i think that's what it's called???) and my vet gave me some stuff to rub on kobi's behind (yeah...YUM) for the prolapse because if it gets worse, they will need to do surgery. SO please,please, please don't wait too long!! Good luck and let us know how everything turns out!