WotLK Lag in icecrown

hi.
so here's my problem , i've been playing in icecrown realm in wotlk for a while now , but these days i have a problem : there's too much lag...big lag might lag you got it...i though it was my connection but no i tried the 2 other realms (lordaeron and blackrock) and everything was working perfectly . i deleted wtf and cache folders because someone told me it could help...and no...i rebooted my modem and the lag is still here...only on my pc i dont know why . Here's how the lag looks like : everything takes too much time when i start running i get back where i was i can't send messages because it takes time to reach the others and this doesn't happen once every 15 mins....it's constant it's always here i just CAN'T PLAY . please if someone knows what to do just tell me
THANK YOU. :)