What should i do about my dog with diareha?

My poor 3 years, 3 months and 13 day old dog, Scruffy, is throwing up and having diaerhia. I haven't made any changes to his food and and hav'nt fed him anthing strange. I don't know if he may have eaten something strange that i dont know about but not as far as i know. I feed my dogs the same things and the other one hasnt been affected by anything.scruffy is a yorksheir terrier miniture and my other dog flash is an american cocker spanial.