Indexing problem please help

The new posts of my site used to get indexed instantly, but about 36 hours ago, I published a post, but it is not indexed yet! I published another post 5 hours ago, but not indexed yet. Webmaster tool shows 106 submitted, 102 indexed.

Any probable reason and solution will be appreciated.

I am using 3.4 WordPress instead of 3.5. Also, installed W3 total cache plugin recently.