What is wrong with my cat?

My can is a little congested. She has been before and the doctor gave me Viralys gel which I started giving her again. She is also sleeping more than normal and is not eating very much. I think that she may have a sore throat because she does not want to eat solid wet food or dry food. I gave her some Halo stew and she ate a little of that. What could be wrong with her? This has been going on about three days. A couple hours a day she acts normal and playful but the rest of the time she wants to sleep or sit around. She is normally a lot more active and playful. She is 1 year old.