Dog is coughing and hacking when he goes outside?

My chihuahua had similar symptoms last December. He has a lot of allergies and it just turned out to be the equivalent to a sinus infection (luckily!). But go get him to a vet as soon as you can- take him to a walk in like the one at Petsmart if you have to. It would be better to get it looked at as soon as possible, even if it was something like a cold.