Hello, First, you should undergo one home pregnancy test to rule out pregnancy though you did mostly safe sex (last week of cycle). Besides pregnancy, late period could be due to hormonal imbalance, over weight/ extreme loss, mental stress, emotional upset, eating disorder. Therefore, I suggest to undergo one USG lower abdomen and hormone test in the absence of pregnancy. You may require progesterone pill to induce period. Kindly, consult with your gynecologist and take advice accordingly. You should control body wt, avoid stress, take healthy low carbohydrate diet with avoidance of fatty food and sleep properly. Be well.