It's important to take your cat to the vet immediately. The symptoms you described could be due to a number of things, including a cold, but they could also be more serious. A vet can diagnose the problem and recommend the best treatment.
Here are some things you can do in the meantime:
* Keep your cat warm and comfortable.
* Provide plenty of fresh water.
* Encourage your cat to eat by offering their favorite foods.
I hope your cat feels better soon!