My cat, Spirit is 4 years old. I have had her since she was a kitten. A friend of mine found her putdoors. Spirit has always been small and thin but she has a normal appetite. Just the last few weeks I noticed she was putting on weight. This week I actually felt her stomach and it is hard and big. I don't believe she is pregnant because although she is not spayed our male cats (2) are. I haven't been able to monitor her use of the litter box. Could she be having a physical problem. She is behaving as she usually does, eating, sleeping and does not look ill at all.