 [ Symptoms ] why am i not menstruating  i am 19 years old and i have not had a period in 6 months i can 100 guarantee i am not pregnant i am not overweight i do not exercise really intensely and i do not really have anything to seriously stress about i moved back in january but i have had a period since then so i do not think stress from that is the problem i have chronic constipation which may or may not be ibs could that be what is causing this i want to make sure before i go get looked at and told that is what it is [ Disease ] not very likely unless it was at the very beginning of your first shot or the end if you havent gone back within the 12 weeks it thickens the womb lining so much that an embyo cant become embedded go see your family planning nurse she will help