Period changes due to weight loss

Here's the thing, back in the day, due to my diet, my periods were always pretty irregular (came every two weeks). Now that I've changed my diet and with that lost 9 pounds within 3 weeks, my period came the other day after almost(!) a month and it's pretty light compared to before. Is this a good or bad thing?

Follow up question, I'm also in the middle of experiencing my 1st plateau which I'm pretty sure is connected to my period. How long do period related plateaus tend to last? Mine's been going on for almost a week now. Is that normal?