|Are you sharing your internet connection with anybody else? If yes, are they downloading lots of data or maybe running a point-to-point sharing program that allows others to download from them?|
If none of the above, keep in mind your download speed is limited by the network and the server you're downloading from. Which is to say, if the network (the internet) is really busy, your downloads will be slower. Also, if the server you're downloading from is really busy, again, your downloads will be slower.