my dog sandy is 16 years old I think lab/chow mix. For the past few weeks she has had loose bowels on and of very smelly. Now she won't eat but will drink she shakes when she walks and seems confused like she does not know us. Last night she was laying on the floor shaking. We have tried to give her wet dog food,chicken and rice and antibiotics from my other dog who is fine. Is this just old age and should we put her to sleep I don't want her in anymore pain. Thank You