Cat walking with head down? PLEASE HELP.?

He is over 2 months old and just recently saw the vet for an Upper Respiratory Infection. He is still on medication (he visited the vet around 2 weeks ago) and hasn't eaten any dry food since then. He has only eaten wet food. And he has peed on some places in the house but other times in the litter box. And now he walks with his head down and lays down with his head also tucked in. But when I put his head up he doesn't cry or show any sign of pain. Any help would be greatly appreciated!