My mama Kat and 1 kitten who is now 8 weeks old. she was born early and weighs about 6oz. I'm having trouble getting her to use the litterbox. I put here in it and she jumps straight back out. I'm not seeing any poop around the house. Her stomach gets hard after she eats her wet food but then goes soft. So I'm not sure if this is a issue or not. So what do I do. Help.