What is my puppies discharge??

I just got a 11 week old Weimaraner. She is pretty well behaved, but has little accidents in the house often. The other day as I was petting her tummy I noticed her "hoo hoo" had some discharge. She didn't have this before and hasn't had it after I saw it this one time. My boyfriend has been feeding her yogurt mixed in with her food. I was wondering if this has had something to do with it?