Have you read Dr. Jason Fungs Complete Guide to Fasting? Since you are not aware of sodium being needed I am guessing not. He also has a blog, here is link to a good place to start reading:
https://intensivedietarymanagement.com/fed-fasted-state/
Your period can have a huge influence on weight, so fasting then is probably not a good idea. You might have more success if you choose another week in the month to do an extended fast. intermittent fasting (14/10,16/8, 20/0 protocols) should be fine,
Also, if you are not short (5’3" or shorter) you are probably at a normal weight range, and it is harder to fast when you have less available fat on your body to begin with, Richard has a calculator on the 2dudes.com blog site, you might want to check that out as well.
http://blog.2keto.com/why-fasting-is-easier-for-some-people/
Good luck on sorting it out.