What caused my dog's behavior to change in just one day?

I noticed a change in my 7 year old male doberman last morning; he was walking with his head low (when I tried lifting it, he cried out in pain), he would lay down out of nowhere with his head touching the ground for like five seconds and then get back up, I also noticed that when he walked, it seemed like at times he would trip over his front two paws if he wasn't cautious. There are a set of stairs (or steps?) that lead into the house and he would walk up but stumble walking down. He eats with a good appetite and drinks lots of water. I noticed he still responds to sound and follows with his eyes (although they look sad). He recently had a vet's visit (he had an infection and is still on steroids and antibiotics) and he said he's perfectly healthy. If I don't see a change today I will take him again but not until Monday or Tuesday.