Hello. I have been cleansing for the past nine weeks and have had not had a menses, except one day this month there was a very slight bit of blood. I asked a young woman who is 30 yrs old, a raw foodist for the past 1 1/2 yrs and a vegan for the past 12 years, if she knew why this happened. Here is what she wrote in an email:
Menstruation: I stopped menstruating during the cleanse, and missed a whole cycle after the cleanse. I then had a two week cycle for two cycles, then a three week cycle for about 3 cycles, and then returned to a 4 week cycle. My period is next to nothing; no pms, no cramps, small amount of bloating. So nice!

I hope this helps.

Don't worry, it is normal. This happens for a few reasons. Firstly, when your body feels that it is not the best time to reproduce (uncertainty of food availability, stress et cetera) it simple decides not to. Also, your body decides what to use its energy on--sometimes it is not on ovalation. If you lost a lot of weight, this also could be a factor. Estrogen is stored in fat cells and low estrogen effects menstration however it does not mean that you aren't fertile.
I am a professional athlete and in the last four years I have menstrated twice. I was very worried at first at did lots of hormone tests, lots of research and saw many doctors. My last period was in October (quite a shock) but it made sense because it was off-season and I was not training as actively as I normally do.
It may take a few months for your body to get back into a normal cylce.
If this continues there are a few great herbs: Don Quai and Vitex/Chasteberry are great for helping regulate cycles.
Hope this helps.
PDeXiting