There is something wrong with my cat, he suddenly very rigid and limping, his back legs seize up and start twitching and when we stretch his back legs out he's fine but when we push them he cries. We took him to the vet who found no injury or anything but 3 weeks later he's got worse. He won't go out and is just laying in his basket away from everyone. He still eats and purrs when you fuss him. I am wondering whether it is something wrong with his insides towards his rear. I wonder whether worms or something could cause such pain?

You had better get that little thing to a vet. It sounds like distemper. I can't imagine the vet you took him to not diagnosing ANYTHING. That isn't right. Of course is purring when you fuss with him, he loves you for heavens sake. Take him to a different vet NOW.

Yes, do get him to another vet ASAP. Keep in mind that cats will also sometimes purr when they are in pain.

Please let us know how your cat is doing now. Thanks!