6 month old hound mix puppy with diarrhea!?

I have a 6 month old hound puppy. Her dad is a black and tan coonhound and her mom is half walker and half redbone. She has always had a very hearty and healthy appetite. About a month ago, she started having random bouts of diarrhea. It is frequent- sometimes waking us up every hour and even every 15 minutes when its bad. It will last a day to a few days and then go away for a couple days but recently has gotten worse. I have eliminated treats and even chew bones and she is only being fed her dry food- Eukanuba Puppy food for large breed dogs. Her food has not been changed recently and she is negative for worms. She has not lost or gained weight and although she still enjoys playing her her best friend- a husky. She does not have the same stamina needing more frequent breaks and is lethargic when her tummy is especially upset. I have set up a vet appointment for as soon as the vet was available. Any suggestions or ideas as to what is going on?