how do i get a flat tummy? is there any kind of medical or herbal pills that cld help without advers effect?

av tried sit-ups and the lots but is wearing me out.had my 3kids by c section so coouldnt start the work out early cos of some pains i had around my lower abdomin. my last chld is 1 now ad am embarassed with my tummy cos am not raelly fat. i need help fast,,,sit ups also gives me back ache!