One Year Old Boston Terrier. He Eats A Very Healthy

One year old boston terrier. He eats a very healthy homemade dog food. Usually VERY active. Yesterday he had bloody diarrhea. We gave him pepto bismol and today the diarrhea is almost completely gone. His poop was almost normal today but had a lot of black in it.... explained by the pepto... but he is extremely weak. He is mentally alert but can't really support himself when standing or walking. He is still eating and drinking normally. There isn't a loss of appetite. I'm very worried. He's our baby. Also, he doesn't have a fever. I can't find anything online about bloody stools and weaknesses without loss of appetite or fever. Please help!