I read in the blood sugar diet book that you can do the 5:2 on 800 calories also. Another option is to do 5:2 with 500 calories for three weeks, then the fourth week you either don't do it, do it on 2000 calories, or do it on 1000 calories whatever works best. Maybe you could add the 300 calories (500 + 300) in the evening when you have your period and see if it helps? Just an idea, haven't tested it.
This happens to me too. My tips are to skip breakfast and have your food as late in the day as possible. Have plenty to drink and try hot drinks to stave off hunger pangs. Do not look at or smell food if you are even slightly hungry. Stay out of the kitchen and keep busy or go to bed. Remind yourself its only till morning then you can eat normally again.
If you find fasting in the day easy but difficult in the evening can I suggest the OMAD (one meal a day diet)? You fast through out the day, every day, but you eat one big hearty & healthy meal at dinner time. I started four weeks ago today & have lost 14lbs. (I also lost 30+lbs on this diet pre baby) & I haven't cut anything out, I've had pasta, stir fry, rice, (even home made pizza twice) I can bare the hunger all day knowing I have a nice meal to look forward to. & I always have a big side salad with it my meal too not for everyone but works for me!