Make you sissy experience the difficulties of having a monthly period, just like a woman. Obviously, biologically this won't be possible, but you can make him go through the same exercises of a few days every month having to wear panty liners and tampon, buy them, carry them around with him everywhere he goes, and changing them constantly. You should also keep him in full chastity during his "period", with no exceptions for release.
The point is to make him understand one of the more uncomfortable and true disadvantages of being a woman the hard way. He will grow to have a whole new appreciation for those times of the month and all the logistics that are involved. It's also a way to humiliate him and forcefully feminize him to a very high degree
You should start a couple days ahead of time, by telling him that in a day or two his period will start and he should be prepared. Tell him that he will need both panty liners and tampons and then take him to the store and accompany him while he selects and buys them under your watchful eye. Make sure you remind him each time he goes to the bathroom to change the items, and make sure you see him bring a new one with him. When leaving the house for any reason, make sure you remind him to have a spare tampon or panty liner with him for while you are out. Check up on him regularly in a random inspection, to make sure he's complying during the full period.
In order for this to be effective, this should be done every month on a regular basis exactly when you have your own menstrual period. There should be no exceptions, whatsoever, period!
Do not let a month or a day slip by without enforcing this, and be very firm about controlling that he's complying through the full period. Don't be disgusted by this, as it is really a way for him to learn one of the ultimate feminine attributes, and besides, it might also keep him from staining his panties from his leaky penis.