I would suggest seeing your doctor and having him/her run hormone tests, etc. just to rule that out. But, as with any change (even one back to a higher fat diet), your body needs time to adjust and to be able to know that you will continue to give it the right kind of fuel. So, it may be that your body is waiting to know that you will maintain this regimen and, once it is convinced, you will begin menstruating again.
There are many plausible explanations-too many to even list-so it would be best to see your doctor, have him/her run some tests, and work from there. Just recently, more studies have come out clearly demonstrating that psychological stress can, in fact, suppress monthly periods.
Good luck, and take care!