I find it much easier to fast if I haven’t eaten too many processed carbs the day before (sugar, bread, pasta etc). Make sure to keep up with water and keep busy for the first little while. Intermittent fasting is an excellent way to start - if you finish your evening meal by 8pm and then hold off on eating until lunch time around 1pm then you have already fasted 17 hours, then in your 7 hours eating window you can have your normal meals. Do this each day and slowly increase your fasting window until you find what works best for you. I have found eating like this has really decreased cramping although I seem to be having longer periods.
If your menstrual issues are heavy bleeding I highly recommend VITANICA Slow Flow - it’s the only thing that has EVER worked for me (I think herbs like shepherds purse which they used on injured soldiers in the war stops bleeding).I first tried intermittent fasting, water fasting, weight loss etc but they didn’t help with menstrual issues (they did help a lot of other issues though).
As far as fasting goes most start with 16:8 - 8 hour eating window and 6 hours fasting per day. Most people often end up shortening their eating window further up to as much as OMAD (one hour window).Otherwise there is 5:2 where you eat normally 5 days a week and twice a week eat only 500-600cals or alternate day fasting where you eat normally one day and then nothing or less than 500 the next.
It’s all a try and see what suits you best kinda thing.In terms of getting through hunger mostly drink a lot of water and tea or some people do black coffee. But also if you go long periods without eating keep and eye on your salt and electrolytes.