Corn Snake Sneezing

[OntheLeuc]

My bloodred motley corn is three years next month, and I've noticed this issue for a while, but honestly haven't had an idea on how to go about it. She's been sneezing for a bit, and it got better over the summer months, but as it's getting colder here again, and the room she's in gets chillier, I've noticed it getting worse. She'll sneeze at least once a day that I notice. There is no mucus or blood spray to suggest it's respiratory and if there's no reason to, I can't afford to take her to a vet.
She's not on a regular feeding schedule, so doesn't shed as regularly as she probably should be. Her 40 gallon is normally low to mid eighties with her light on, but gets cooler at night when I turn it off. She always has an undertank heater on, but seems to be avoiding it for hiding in the foliage at the other side. I moved the foliage closer to where the lamp hits during the day so she gets a bit more warmth, but nothing has helped with the sneezing. She uses aspen shavings for bedding. Someone once suggested a black light lamp?
Any help is appreciated.