Has your cat been tested for Feline Leukemia? That's what would worry me. I had a cat once with that exact presentation, and found out he was dying.
If so it's not necessarily a death sentence, it just means you have to take extra special good care of him, keep him separate from unvaccinated kitties, and be aware that he might not have a "normal" life span. And be relatively expensive.
But chances are your kitty just has a cold. Three of mine have been sick recently, eyes watering, sniffling and sneezing. If she's still eating and drinking fairly well I wouldn't worry so much, but if not, take her in for antibiotics.