What is wrong with my Doberman?

My Doberman hasn't been himself these last two weeks. The vets in my area are very costly and there are plenty of experts on here so I thought I would consult you all. His symptoms are that he is very lethargic, has a runny nose, seems to be creating lots of saliva all the time and he always wants to be chewing. I hope it isn't serious, he is a bit of a nuisance and has already cost me a fortune and it's the last thing I can be bothered with.