Same thing happened to me, my last period was late by one week. I guess it has to do with your body being under stress, if you think about it you’re putting your body in a state of scarcity and it might slow down some processes, funny thing my period came after my refeed. I say is part of the detox processes and the things that happen during prolonged fasts
There’s lots of reasons besides pregnancy and fasting that would cause your period to be late. Have you ever used Depo? That BC piles up hormones in your fat while causing weight gain. When I lost weight post depo my hormones were all over the place for a while. Hormones were being released as I burned the fat. Other BC could do the same thing. I’d look into it to ease your mind. Hormones, stress, medication, whatever it is, at your age it’s not likely to be a huge or permanent issue. I’d keep on working towards your 8 weeks. Attain your goal. If your period is still off and the fasting was the issue it’ll go back to normal and you’ll know.
Are you at all stressed? I am super regular too and once my period was late and it stressed me so much that it ended up coming 1.5 week late. But it came. Luckily that has only happened to me once. As for fasting I’ve done a super long fast and 3-7 day fasts and never had a problem except that once.
When fasting you’re likely hitting ketosis. What you’re experiencing is a common story on the keto boards. As you enter ketosis and are burning fat you’re liberating hormones stored in that fat. So the period gets wonky- off schedule, appears or disappears, weird blood, heavy, scanty etc. Usually sorts itself out by 3 mos. If you are sexually active, do take a pregnancy test regardless of your birth control usage. If you’re under life stress or had a birth control or medication change, these could be other reasons. But it is possibly related to the fasting for the reasons outlined above. If so it’s just recalibration.
I’m keto, not on BC or any meds as well and normally do 48s then OMAD. I was pretty regular within a day or two but with longer went 10days late last month & 5days late month before. With huge diet/intake changes the body changes to adjust. I carry around my travel tampons around the time I’m supposed to start to accommodate.
I have experience with water fasting and never experienced this….although I only installed the Flo app after that point in my life, and it has been a few years so I can’t be sure it was cosistent. In my current fast, I actually fasted through menstruation. Talk about pain. I was supposed to start yesterday according to Flo, yet I still am not experiencing the usual symptoms I get before it starts. I’m on hour 78/120 so let’s see how this goes. Also, I broke out for the first time in years a couple of days ago and noticed some hyperpigmentation on a sensitive area on my face so it could be my body under stress/clearing out the gunk.