Thank you for submitting your question regarding Blacky. I recommend seeking veterinary care for him as soon as possible. Several weeks is way too long for a puppy to go without proper nutrition. Based on his exam findings, fecal testing will be recommended to look for any intestinal parasites or other intestinal infections. Based on these results, either treatment can be recommended or further testing if necessary. He may require deworming medication, antibiotics and fluids to rehydrate him. I hope this information helps!