My cat has been sneezing and now has a runny nose.

I suggest taking your cat to the vet for a check-up. Sneezing and a runny nose can be indicative of a respiratory infection, allergy, or potentially something more serious. The vet will be able to diagnose and treat any underlying issues, as well as provide advice on how to manage the symptoms. In the meantime, make sure your cat is well-hydrated and comfortable, and keep their living space clean and free from allergens.