Minecraft lagging problems?

When I play minecraft on single player it will be all fine and everything works fine. But when i play on multiplayer i will say something in chat and it will take 10-20 seconds to appear. Also i tested this by falling from the sky to the bedrock and then i was walking around for a few minutes then finally died. Also when other players are around me they will say they are right next to me and yet i don't see anything. And yes i've tried disconnecting it has nothing to do with it. So can someone please help me this has been ******* bugging me for 3 months. Thank you =D