I asked a previous question, which was answered here, which answered my question, exactly as it had been asked.
\chead{\ifnum\day < 15
Mid-%
\else
End-%
\fi%
\monthname[\the\month]%
}
However, this isn't exactly what is required. What I need it to do is give the name of the previous month if it is the first 15 days of the month(ie. today would still be End-August) and give the current month if it is greater than 15.
Have tried creating a newcommand for \prevmonth but can't get that working.
\newcommand{\prevmonth}{\if\month=September%
August%
\fi%
}
Any help would be appreciated!

Midis still necessary. If this would have been explicitly stated, I would have provided another solution :-( – Sep 14 '16 at 15:59