Lips licking in dogs is usually associated with stress and nervousness. As your dog is also isolated which is another sign of stress, so, there are chances that your dog is having stress.
Another reason of lip licking is excessive salvation or drooling which can be due to some specific stimuli like food, excitement etc and some pathological conditions like like gum & dental diseases, tongue injury, stomach disorders, mouth ulcers, tumors in mouth, and due to some metabolic disorders.
Lip licking in dogs can also be the part of self grooming because dogs can clean any area of the body including lips if dirty.
So, you should ease out stress of your dog or visit a vet to get advice.
Your question is not clear, you said the vet said to "Leave him over the weekend and bring him back on Monday." Leave him where? The vets? Bring him back on Monday? If you left him at the vet over the weekend how can you bring him back on Monday. He will already be there.
Also, hurt or poisoned are both very broad and different diagnoses. Which one is it and which one did your vet say your dog had. If it is poisoned, I hope to God you left the animal with the vet because you do not sound like you really know what is going on. And licking of the lips accompanied with isolating himself is usually poisoned and bleeding internally and if not handle asap is fatal. Is he throwing up blood or have bloody diarrhea? There has to be more symptoms that you are not picking up on. But yes, you dog could have been poisoned. Now go around and check your house for any products you may have left out or any bad food the dog may have ate.
The licking is from nausea--this can be secondary to pain or a disease. Lack of sleep further confirms your dog is painful. Your dog needs to be examined by a veterinarian to determine the cause of the nausea. It is possible it is related to a primary gastrointestinal problem, secondary to other conditions, or from pain from a trauma. Your veterinarian will help determine the cause of your dog's illness and start appropriate treatment.
Your dog may have something stuck at the back of her throat and is trying to push it back with her younger. Or maybe she's trying to stop herself from throwing up.
