Too many mobs are spawning

I was in my single player world and ,when I looked into an unrendered chunk, i saw MANY mobs in caves (day time).When I realised it, I went to the nether to get myself some wither skulls and when I was going to the Nether Forretress,I found a place that spawned many zombie pigmen.I've searched for this issue,but i could not find any other person that posted it