Xbox live major lag problem! please help!!!!?

i have a problem, when-ever i want to go play mw2 i join a game and i keep getting 4 bar connection at the start then it goes down to one and keeps swapping between 1 and 2 bars, but the thing is, my speed is at 19.20 mbps and it was fine yesterday, and when matchmaking it says the game i am joining gives me <50msping which is the lowest on the 360!