i think you KNOW the answer is related to your diet and weight loss.
are you at a healthy weight now?
if so, stop trying to lose weight is my advice.
even if you are overweight, i think you should stop losing weight at such a fast rate - you body OBVIOUSLY doesn't like it.
if you're underweight, the answer is obvious. try to put some weight on and consider why you were trying to lose it in the first place.
i lost my periods at a healthy weight through unhealthy methods of losing weight. 2 yrs on, i've only had 3 light periods, gained to a healthy weight... and still nothing. take this seriously and sort out the problem sooner rather than later. i know how easy it is to just put it out of your mind.
hopefully if you maintain your weight (or put some on, if necessary) for a while your body will get more comfortable again.
my doctor said the only way to get my periods back was to put on weight.