Trying hard to not get disheartened : (

So a couple of weeks ago I decided it's time to lose those last few annoying kilos ( I'm in Australia) so joined the gym and then a week later stumbled across this wonderful site.

I've been tracking my weight and measurements the entire time, and eating well below my calories most days, and excercises heaps..... BUT..... nothing is happening. I lost 100grams on the scale and nothing in my measurements.

Sorry for the TMI, but I also got a random period ( not due for another 2wks ) and now just cramped and feeling miserable, which is not normally how I am either.

What am I doing wrong????????
Help please!