ATB on "Website loading extremely slow"

Hello,
For some reason my website became really slow, it takes 30-50 seconds to load any page and before it was under 3 seconds. Disabling all plugins won't make any difference. A assume it could be NextGen photo gallery related issue for the following reason: If I restore website from 1 month old backup it runs fast but within few hours becomes slower and slower but when I restore again and disable NextGen plugin it it runs fine. Other websites on the server are working fine. I also tried to run site speed test but it won't run, gives me an error all the time. Any ideas on how to ID the problem and fix it?
http://alextravelblog.com
Thank you!