I just got a new rabbit about 2 or 3 weeks ago from his previous owner. After about the first week I noticed he wasn't drinking, so I changed his water bottle to one with a bigger sized nozzle and he has been drinking very frequently, especially at night.
He's been also scratching the bottom of the cage at night, he does it occasionally throughout the day, but not as frequently as he does at night. I noticed this morning that he started sneezing and he has been laying spread out on his stomach closer to the front, whereas he would usually lay towards the back where it is darker.
After he sneezed for the 6th or 7th time, I picked him up and sat on my bed with him. I noticed he was breathing very fast and loud compared to my other rabbit. I might just be overreacting, but I've had rabbits before and I have never encountered this problem.
I feed him Wild Harvest Advanced Nutrition Diet for Adult Rabbits, and I give him these mini rolls of timothy hay. I use Purina Tidy Cats cat litter the Glade tough odor solutions one, I just recently changed their litter because it was cheaper for me to buy it in a bigger size than by a 3 dollar bag and use it in one day. I use these for both of my rabbits and he is the only one showing alarming symptoms.
My rabbits are different breeds, my female is a lionhead and the male, whom I am concerned about, is a giant sable mini lop.