My website starts well and after few days of access it goes terribly slow. Is there any module or any external tool to check the performance of the drupal website. So that we can point out where we are facing issues in drupal so that we can solve them. My pages are built out of average 5-6 views, does this effect the performance of the website ?
You could try new relic, it will give you insight into how expensive database queries are or where you have a bottle neck which is slowing down your site. It has some integration with Drupal and could also show you if you have a problematic module...
Also if your pages use a lot of views, have you tried caching the views? It is part of default views module, go into your view edit under "advanced" on the right. Click caching and turn this to time based. This means that rather than running each view query / view rendering on every page load - It will run it on the first load and retrieve a cache until it expires. The caveat here is that you will have a lag on the results for how ever long you choose to cache.
XHProf is capable of reporting function-level call counts and inclusive and exclusive wall time, CPU time and memory usage. Additionally, it supports ability to compare two runs (hierarchical DIFF reports), or aggregate results from multiple runs. Originally developed at Facebook, XHProf was open sourced in Mar, 2009 (source)
I'm using it frequently and it really helped me find some bad bottlenecks.
You may use the Boost module. Here is more info on it: http://www.onyxbits.de/content/quick-drupal-performance-test-boost-module-makes-huge-difference.
Boost provides static page caching for Drupal enabling a very significant performance and scalability boost for sites that receive mostly anonymous traffic. Boost is very easy to install and has been throughly tested on Shared, VPS and Dedicated hosting. Apache is fully supported, with Nginx, Lighttpd and IIS 7 semi-supported.