18 pounds and no period

Hi all,
I'm a little concerned about my Water Fast and wondered if anyone might have experienced this? I just came off of a ten day water fast. I began with a three day juice and raw food fast, did the 10 day water fast, and then ended with another three-day juice fast into raw foods. I've lost 18 pounds in this time but I have no period this month. I am now two weeks late - (I'm not sexually active).
I guess I'm concerned it because I researched the Water Fast quite a bit before I began and tried to do it very healthfully with a transition in and out of it.
Is it because of the rapid weight loss or could something more serious be going on? Have I depleted to many minerals/vitamins?
Any input would be appreciated.
Thanks all!