Could being outside in the rain all day contribute to my dog being sick?

My dog spent most of Saturday lying outside in the rain (he had shelter but chose not to use it) Today he is a bit lethargic, not too fussed on his food and has a fever. He is not bad to the stage I would take him to vet, as he can still run around, bark and play with his toys (Obviously if he deteriorates I will take him to one) I know that you cant catch a cold from being out when its chilly, but just wondering whether I should keep him inside when it rains as well?