Is this normal? Please help!

So I have been pretty grumpy and sometimes might even cry after the short ''high'' from the excersise is over, really dont know why. I do some kind of workout for legs 6 times a week, sometimes 15 minutes a day, sometimes 30. So the day before yesterday I did my normal 15 minute leg workout (Youtube: XHIT daily miley cyrus legs) and I didnt even break a sweat and my muscles didnt feel anything, just really lacking power. I decided to ''let my muscles rest'' for one day. Today i did the routine again, I started sweating almost immediately, it felt good in my muscles and I was able to push myself again. Does this mean i have been overtraining my legs, too little carbohydrates or what? And + ive been on low carb for a pretty long time(first around 40 gr/day for a month or so and now ive been more like 70-100, does it mean that if im not grumpy or angry or exhausted im not losing fat? Some days i eat more carbs (slightly over 100) but i feel like im automatically gaining because ive heard you need to be carb deficient to burn fat?