I think my cat is sick, any ideas?

My cat has been really quiet today and yesterday. She's gotten a little fat but I don't think shes pregnant. She is shedding fur like crazy which she hasn't done before, and shes not eaten or been outside. She eats like clockwork every morning generally 2-3 cat pouches plus maybe a treat. She's refused treats and hasn't left her sleepin all day. She normally goes outside for a few hours a day regular as clockwork because we don't have a litter traybut shes hasnt been outside for a long time. Any ideas? Or am i just being a worry wart