My cat has not urinated in three days

I, f16, have a cat, 12m, who is currently on "hospice" as he has lymphoma and we want to keep him for a little while longer. However, we've been presented with an issue. He has not urinated in three days. He has been hydrated and everything, but he simply doesnt leave the same spot hes been in to do anything but eat or drink. And no, he has not gone on the floor. Im scared, and my mom will not take him to the vet again for this. I really just don't know what to do.