Constant Pigman attacks

I keep getting attacked by ALL the zombie pigman every time I enter the Nether.  I ignored the Nether for a Minecraft Month or more, and when I came back they all attacked me.  No idea why.  I ignored it some more and then got the same result.  Today I entered, got attacked, lead the pigmen to the overworld and waited until they calmed down and stopped attacking me.  I then re-entered the Nether and again got attacked.  Please fix...I need to kill Endermen and get blaze rods!