Basically, I agree with Craftlady. Just a few things to add.

My Vita is prone to URIs. We are lucky to get 6 weeks between bouts. The vet tells me a herpes virus has taken up residence and is not leaving any time soon. This has been 9 YEARS of it. She has had teeth cleanings, no teeth issues. It is frustrating; and the best I can do is to get her on the meds right away, so it clears. And at times, the 10 day therapy is not enough and I have to give her Clavamox for 14 days. So we go 2 weeks of meds, pray we can get 6 weeks relief, then back on the meds again. Sigh.

And while URIs are contagious, in 9 years of this, I've only had one other cat have a URI and only once. Go figure. Does this mean it isn't a URI? Maybe but then what the heck IS it???

That was my other thought. Hairballs, and tooth issues, could bring on the symptoms. If you don't already, consider using a hairball treatment -- either food with it built in, or one of the gels out there. It shouldn't hurt, and may help. Tooth issues, well, only a dental exam can tell if that is the problem.