I don't know what is wrong with my puppy. Help me please!!!

My 4 month puppy woke up this morning wit lost of appetite and lost of enegy. Yesterday he was fine wit tons of energy and eating good. He got his shots and his chip put in a week ago. He just look so sad. He doesnt eat or drink anything and wen i pull out da leash he gets all excited but i kant take him for a walk cause its cold and raining bad, I even tryed playin with him inside but he just lays there and if i call him he just lays there to. I just want to know what is wrong wit my poor baby.

[Aleda M Cheng, D.V.M., C.V.A]

If the problem continues please take your puppy to the vet.  Unexplained lethargy and loss of appetite could be caused by hypoglycemia, upper respiratory or other infections, parasites and more.