Thanks for the reply forestborj,
Before this slow down happened I had none of these plug-ins installed and the site loaded just fine (while i haven't made any changes to the site), so I'm trying to solve what is causing the slow down without using plugins which might just mask a real problem with the site.
I just checked my site on gtmetrix.com and it got a 92% on Page Speed, and 78% on YSlow.
appreciate your help..