Diet help ??????????????????????

Hey, Im 16 years old and a female. Im big boned and about 5'5. I get told alot i dont look that big and sometimes in the right clothes im happy with myself. Im 14stone but get told by doctors and everything one else i dont look as big as i way on the scales, i have a friends whos at 10stone and about the same size as me. Does any body have any good diet ideas, ive tryed a calorie counting diet before and i didnt find it worked very well. And ive also tryed the atkins diet but everytime i just make myself ill. I also tryed not so much starving myself but eatting breakfast lunch and tea, but tiny and i mean TINY amounts but because i suffer with headaches i tend to get them alot. i try to do as much exercise as possible aswell. But im just one of those people who take ages to lose weight but puts it back on in a flash. hellppp!!!:)