sounds like allergies. Havoc will sneeze this time of year. I have allergy pills I give him after a day or two but if it's allowed to linger without meds he'll get the boogers and such about a week later and it keeps getting worse until he needs antibiotics. I went through 3 different vets treating him for constant "upper respiratory infections" before I finally found one that diagnosed him with allergies. He's been fine since.

I bought a little tabletop air purifier and that helped out a lot. Just a WalMart cheapie, like 30 bucks or so.