The PMS Assistant is a great app for you boy! With it you get warnings when your girlfriend / signifier / whatever friend will be in the worst days humorously. It is useful to warn you and give you tips on how to behave during this period in order to survive this phase.
How it works: you enter the name of the person you want to receive warnings and the date of the last cycle, from that PMS Assistant issue alerts whenever the PMS start. Also you can follow the tips to do and not do these days.
Now you can see the fertile period too!