This is usually a problem with your server. My sight got unrealistically slow one day, and it was because I had tons of request and hits on my server.

So what host do you suggest and what server do you suggest?

Topic was moved from Custom Code Modifications.

Nirmalya, you can check recommended hosting companies here http://www.oxwall.org/hosting . Getting dedicated server from any of them is the best option.

Some plugins when wrongly configured can also make the site slow.

For example when you enable the "Logged in users check" option in "Anti spam" pluign, it will slow up the site to a greater extend.