I always loose weight in pregnancy. Admittedly I have it to loose. DD I started at about 92kg and lost 10kg from when I found out I was pregnant to the start of the 3rd trimester then my weight plateaued because what I was loosing from "me" was balanced by the weight I was gaining with DD. After having DD I ended up at 70kg.
With DS it was very similar again - I started at 95kg, lost 10kg through the pregnancy and then lost another 5kg when I had him to end at 80kg.
I was diagnosed with GD at 32 weeks with DD and 12 weeks with DS. My Drs told me that with GD you tend to lose weight because you have to be so much more careful about what your eating and portion control etc so that may explain some of your weight loss. You've also had a fair amount of stressful things happening in your life over the last couple of weeks which may be contributing to the loss of appetite/weight loss too. Obviously its not "ideal" to be losing weight when pregnant but, so long as you are eating properly and healthily and not actively dieting it shouldn't be a huge concern. Like always though, if you're really worried about it, talk to your dr about it or the diabetic educator/dietician that you are probably seeing for the GD.
Hope that helps.