My dog is 4 years old He has gotten very sick and I cannot afford to take him to a vet. He has become very tired won't eat and is drinking some water but not much .He is an outside dog he has had all his shots. I went and purchased some penecillin to see if that would help but his condition is not chaging

With those symptoms, it could be many different things. If you are in a large city, check around, there may be a low cost clinic you could find affordable help. Otherwise, keep him comfortable an hope for the best. If it is a viral infection, not only would the penicillin not help, little else could either.