Run a internet speed test:http://www.speedtest.net/
If you get lower than expected then you are:
a) consuming bandwidth (filesharing)
b) your line sync is lower, this can happen if the isp botches maintenance, or has decided to cap you
for a) check your upload and make sure you cap your upload. The problem with p2p is that it requires upload which saturates your line with ACK packets which impacts your download. Something like nntp eliminates that and you can download at line max and not have normal net overly impacted.
for b) you need to reboot your router, and if it keeps syncing lower phone your isp. its rather complicated but often the isp fucks up.
If you are on wifi, try moving to ethernet.