1/It could be the computer needs a good clean up
2. It could be your ISP is particularly popular[busy] one
3. It could be your particular situation with regards the type of connection you have and and the distance your are from the exchange.
Starting with 'Could be' 1
Download Ccleaner[click here]
and install and run it- this will sort out the accumulation of Temp file associated with the Internet.- it will mean probably you will lose some cookies and bookmarks - so you may be logging onto sites afresh here and there
2 and 3 . You do not mention your Computer spec or the ISP both useful info for us to analyse the problem in more detail.
So when you come back all the detail so that we can go further