For monthly drawdowns your ARF payslip should show 4 or 5 class S contributions per month, depending on how many weekly periods were in each month.
Are you sure the 5 contributions are not just for May ?
It doesn't matter whether you are making weekly, monthly or yearly drawdowns, you will be entitled to 52 class S for the year provided you have drawn down at least 5000 euro.
If there is an error on your monthly payslips and at the end of the year and you have less than 52 class S contributions showing, you should contact DSP to have the error on your Prsi record corrected.