Something is wrong with my dog?

I have a three year old Great Dane named Miles, over the last hour or so he has been acting really strange. He is drooling A LOT (He normally doesnt drool unless he is excited), his ears have stayed pinned back against his head, he is coughing/gagging a lot, he won't stand up but he will crawl over to me if i call him, he won't eat his lunch or drink water, his tail is tucked between his legs (but he will wag his tail a bit if i talk to him), and his stomach is hard as a rock. Before that he was running around and playing like his normal self. He is normally very active and playful, so this is really strange for him. I can't take him to the vet right now and no one else can take him either, i am only 14. Maybe he has an upset stomach? Any ideas on whats wrong with him and how i can help him?