Hi I am 26 years old and often had problems with feeling faint but within the last 4 months its become a lot worse- iv been feeling weak like i am going to faint several times a week and have to eat something like biscuits or bread to stop the feeling. When i have eaten this and stop feeling weak i get a bad headache and feel tired. I feel i can sleep yet am always tired, im always thirsty and keep feeling really hot. iv put on about a stone in the last 6 months and often my eyesight will go blurry. I have had my blood tested and its come back negative- what else could it be?