I have a Sitecore instance Version 8.2 Update 3 in my local PC. When the CMS or live is not visited or idle for a while and I browse it again, the page doesn't load and shows this error:

> Cannot open database "MySiteSitecore_Web" requested by the login. The
> login failed. Login failed for user 'sa'.

After refreshing a few times or loading the page in another tab, it then shows this error:

> Timeout expired.  The timeout period elapsed prior to obtaining a
> connection from the pool.  This may have occurred because all pooled
> connections were in use and max pool size was reached.

Again after refreshing the page or loading it in another tab will finally load the CMS/live site correctly.

It was working fine but recently started behaving this way and this happens frequently.

What could be the reason and how can I fix this?