Hi, I'm so sorry you're baby is going through this. It's hard to watch and you feel helpless when they don't feel well.
I also don't have any experience with URIs, but it looks like everyone has you covered with great advice. Keep an eye on him, continue his meds, follow up with the the vet, but take him back before the 7 days if he seems worse or is not getting better. The steam showers will help to loosen his mucus, and help with his cough. I hope Tank feels better soon. Please keep us posted. Feel better buddy. Sending love, hugs, prayers and positive thought.