What Causes A Delayed Menstrual Period,weight Loss And Fatigue?

I have been experiencing weightloss, fatigue, low blood sugar, abnormal periods (I am two weeks late and I am not pregnant) increased urination and salt cravings. I am having a hard time getting in to see my doctor but my blood sugar has been extremely low (below 60) and I keep getting headaches and I feel like I am going to pass out when I stand up even if my sugar is ok. What could be going on? (I am really moody and down because of all of this, I have 3 children and no energy.).