I am sorry you are not doing to well mentally. I am sure you are strong as a horse physically!
Often when you are faced with negative thoughts and perceptions, you are now in a negative state of gloom and misery. If you have a positive mind set, you will see wonders. Keep yourself occupied. Don't try to over work yourself though. Read a book. Sit outside in the sun. Rest. Release yourself from the world. This is the perfect time to attend to your needs and be responsive of your body's needs. If you believe in God but not a church goer, now is the time to get closer to him.
I started my fast this Saturday. I am going strong. I can't be weak. I have three small children and a husband. Every day I am faced with temptations. I have to prepare 3 meals a day, every day. I have to serve my family. I have to clean the mess. All while enjoying a refreshing glass of warm water sipped through a straw. I never realized how good water tastes!