MoP Latency

I am having problems with MOP latency. The latency seems to be too high( about 1K-3K), only in MOP itself, i have test the latency in CATA, but the latency and frame rate are fine, even fast sometimes. I have noticed an abnormal thing about my PC. MOP, when i first downloaded and played it, it was fine, and play experience was good, but then in 1 day, i remember it was Thursday, MOP worked like a superman, it was really really fast. But in the next day, i witnessed a serious breakdown, the game was slow considerably, the latency started to increase everyday. I have tried to fix and done anything that i could, but the problem still existed. I really hope someone can help me fix it. I miss the game and i just want to play it again and get rid of the latency problems.
Thanks alot for reading!