version 3.5.1, CPU overload, 505, 503 error, slow site

Hi everyone.

I am running a wordpress site with about 300 visits per day and max 1500 page view.

I have the following plugins:

wp-jquery-lightbox
Wordpress Statistics
Simple Local Avatars
Really simple Facebook Twitter share buttons
Pie Register
MediaElement.js – HTML5 Audio and Video
JW Player 6 Plugin for WordPress
Hover Image
Faster Image Insert
Anti-spam

and I am using headway theme 3.4.7.

Ever since I updated to 3.5.1, I have been running into a lot of problem. My site went down very often (Everyday recently) and I have a slow site every one and day. I ran into 505 and 503 error a lot, and it is just annoying.

At first I thought it is the problem with my hosting provider (Hawkhost – I am using their shared plan), but they told me the unavailable of my site is due to the overload of CPU usage. I checked the log at my cpanel, and I do find that it went up to 100% every now and then and sometimes 50~75%.

Can anyone help me so that I can avoid the CPU overload? It is very upsetting to always find my site offline ??

Thanks in advance!