First, has it always been this slow or is this something recent?
After you answer that... There are a lot of things that can slow an Internet connection down, primarily starting with how you're physically connected to your ISP and DNS. If your phone line is copper instead of fibre optic, if your phone relay is densely populated (e.g. By a block of flats), if your telephone exchange (or cable service) is experiencing heavy bandwidth (peak times). And that's just the line - it says nothing about the ISP, the servers, your own local network, your router/modem, or any satellite relays between you and the server.
The best way to investigate the cause behind slow internets... Call your ISP. They should be able to tell you if anything is off on their end, and if not, they should be able to track down any interfering factors along the line.