why dont i lose weight

ok i had let my blod test done and the doctor said something about thyroid but icant remember and i even got some tablets.but what it is exactly that you dont lose weight?
and second i have left my regular meals like i first used to eat just an apple for breakfast and now cereals and in the afternoon i eat(normal) and in the evening sometimes i just skip it and drink milk and eat salad..
is there now any way to get back normal muzna or the others?please help its a serious problem because i have done everything but…even when i was in pakistan i just ate something in the afternoon and that was it.and i onlyy lost 1 kg in one month and there i had a lot of exersize.its not like that i didnt move.