Before assuming that the cat is mad at you, I would take the cat to the vet and get a urinalysis done to make sure that there's no bladder infection going on. Please do this first! And, if you get the all clear, then you know for sure that the cat is not a happy camper.
Good luck!
If I got pinned in the corner by a Saint Bernard I think I would be pretty mad too. You need to train your Saint Bernard to leave your cat alone. A Saint Bernard is way to big of a dog not be better trained.