Question

Hello my name is Tanya . I have a four month old black/brown lab chow mix puppy, he just recently came down with something. He was fine last night, woke up to him acting weak and ill. Here are his symtoms: Hard time walking (like hes aching in the hind) , not wanting to play or interact, very tired , his head seems a lot warmer than normal, not wanting to drink his normal amount of water( he has eaten however), keeps swallowing hard and sticking his tounge out as far as he can. What could this be? I would appreciate any help that you could give me. Thank you.

Optional Information:
Age: <1; Male; Breed: Lab/chow mix

Already Tried:
Ive tried to get him to move around or go outside thinking maybe fresh air would help but he seems like he can bairly walk. I also usually dont let him on my furniture but because he was ill I thought Id try to call him up into the chair, he couldnt jump he just fell over. I have no clue what is wrong with him but if it is possible it is life threatning I really need to know. I know I should keep fluids in him which I have got some in him but not nearly close to his normal amount of daily fluids. He has eaten , hasnt thrown up but his stomach is making this terrible sound.