Hey Francisco,
You mentioned your website has only been up for three months so it's fairly new...
My guess would be that Google is possibly still working out your websites page rank. I reckon it will be up within the next month. I honestly have never had this problem.
Also, if you don't of know this,
http://www.newbie-business-guide.com/ and
http://www.newbie-business-guide.com/index.html will most likely end up with differen't page ranks

So one may be 0 and the other maybe 5...
At the moment I see both pages mentioned above as PR 3.
Hope that helps
Tech