did you change anything around the time the speed dropped?
can you still download fast from websites etc?
and make sure the port is forwarded if you have your router firewall on.
Also 1 great way to check if it's about the torrents or something else, take a few torrents at the same time and see if the speed goes up. If it does then it's just a problem with the seeders in the torrent, lots of seeds doesn't always mean good download speeds right away.
And might aswell check the settings to make sure no one has set a download limit there. Also are you getting lots of connections (like 15+) to the other peers?