"my dog is 5 months old and he recently has been acting really weird. Hes been coughing a lot and he wont eat as much and he use to and also he really doesn't have that much more energy anymore he also has a very dry nose I'm really worried"

He could have kennel cough. Please take him as soon as possible to the vets to get properly checked out. Dogs do not cough as a rule. He sounds sick especially if he won't eat. Please don't guess on this as he could get very very sick, very quickly and then you could lose him totally. I love GSD and I hate to see you lose him.