Bloody rear end

This past Sunday I noticed my 4 month old kitten, Abbie, had a very bloody butt, with what I would call a bloody butt booger attached to it. It wasn't like it was hanging out of her rear end, it was just stuck on the outside of it because it was mucousy (sorry gross). I freaked out and called the animal hospital. They said to keep an eye on her and notify my normal vet in the morning. She was acting fine, playing with her sister, eating and drinking (she's obsessed with the tub and water bowl). So Monday morning I called my vet and they said to just keep an eye on her. I haven't noticed anything since then and she's been her normal crazy self. Well today (Thursday), I was getting ready for work in the bathroom and Abbie went into the litter box (in the bathroom as well), I noticed she was taking awhile, so I kinda kept my eye on her. When she got done she ran out into the living room and a drop of blood fell from her butt onto the carpet. I picked her up and there was another drop coming out . Other than that her butt wasn't bloody. I found the stool and that was bloody. I called the vet and my boyfriend is taking her there today.

Has anyone else had a similar experience? I'm freaking out - mainly because I don't know whats going on and my boyfriend hasn't responded to my texts. Her sister hasn't had any of these symptoms and I just took them to the vet last Thursday to get their rabies shots and their feline leukemia shot. The vet checked their stool - they had coccidia when I first adopted them from the shelter - and on Thursday the vet said the stool was fine. I haven't found any worms or anything in their poop otherwise. I have no idea what else is going on. I feed them dry kitten food, her poops are smelly, but I assumed that was normal.

Hello ,
Maybe she's not digesting the dry food very easy try mixing it with a Little bit of wet food or switching her food I had a similar problem with my kitten and dry food I just mixed it with a Little bit of wet and it seemed to help him a lot .

I've been feeding them the same food since I've adopted them, so could the digestion problems start randomly? I never noticed this before. 

My boyfriend just called and said the vet has Abbie and is running some tests.

I'm glad she's at the vet.  It could be from parasites to sensitive tummy issue.