internet speed on macbook is very slow

i have a macbook 2.4Ghz intel ,my wireless router is fine.DOWNLOAD speed is 9.36/mb/s,Upload speed is 0.55mb/s..but recently when i surf internet the speed become super slow,really dont know what's wrong.the safari sometimes open a page need take 1-2min,sometimes it just show cant connect to internet.i check the network speed of airport it shows 0-10Kb/s sometime,and it never load page.....but some lucky days it will become normal....pls advise me how 2 solve the problem,thank you v much....