Hi I Am Nearly A Week Late For My Period.

Hi I am nearly a week late for my period. I am definitely not pregnant and have also been constipated on and off for over a month. I haven't properly been without medications like laxatives to help in weeks. I feel quite bloated sometimes. I have been trying to loose weight since September and have lost 4 and a half stone. However this is the first time I've missed my period since I started at 10 years old. I'm not regular to the exact day I can be a couple days early or late but this is definitely a lot longer. My last period started on 27th of Feb. The last 2 months I've eaten between 1300 and 1700 calories which compared to when I first started dieting in September I was only eating max 1000. I don't understand why this month it's not come. Plus I was more regular with my bowel movements at the beginning of my diet than I am now. It's been over a month since I've been going to the toilet regularly as normal. I find I have to take laxatives or medication to help me go quite frequently