codeigniter condition

[eluser]alexaaaaaaaaaa[/eluser]
Hi, i'm new with CI and i'm having a big issue with a condition...i know i know this is dummy
but here's what i need
I want users to be able to posts only 2 articles per month.
When the user submit an article i store in the database the date (time) when it was created.
SO....when they will try to post the third article i have to check something like this...
if($this->input->post('standard_project'))
{
///here's where i have to check him if the user has more then 2 projects posted in one month


}

the only thing i have managed to work is that he can't post more then 2 projects...
Please help me!
Regards,
Alex