Raising happiness in Pokémon Sun / Moon is a pretty annoying task for a lot of people, but there is a nice trick that will make it happen very fast and easy. With this method you can evolve Munchlax or Pichu very easy.
What you need to do is buy a lot of TMs for the Pokémon you want to raise happiness with. Buy lots of two different moves, such as 50x Move1 and 50x Move2. Now teach this to the Pokémon, and use these two to juggle between the two moves. Each time you teach it a new move the happiness will increase. So teach it Move1, then replace it with Move 2, replace this with Move1 again, and keep doing this for 10-15 minutes to get enough happiness to get it to evolve. Note that you need to also level it up once you reach the desired happiness before it will evolve.