I Just Had My 12 Week Old Male Kitten Neutered

I just had my 12 week old male kitten neutered yesterday and he is eating, drinking, playing and being a normal kitten. But now he won't use his litter box and when he went poop on the kitchen floor I noticed that there were drops of blood on the floor as well. Is this a normal thing for a newly neutered kitten and is it life threatening.