hi . last month my period was 2 weeks long when it is normally one, it was very dark in colour, almost black and a bit lighter than my usual period. this month my period is a week late. although its not entirely unusual for me to miss a period i am a bit worried. i am underweight for my height and ive been getting my period for 4 years. i am 18, about 165cm, 47-ish kilos (i find it hard to gain weight), no medical history