Your best bet would be to call the vet as soon as you can. Please do not try any type of home remedies, this may make the situation even worse. Some dogs face this problem due to some disease as big as cancer while some dogs face it due to some small infections. Please try to take some time out for your faithful buddy. You can get some help from the following website also.
animalpetdoctor.homestead.com
animalpetdoctor.homestead.com