I would say your carb intake is a little to low. I would have gradually decresed my carb intake from 100g and lowered it gradually. As you have gone for such a low carb intake and have managed for 3 weeks, I would recommend sticking with it and your energy levels will come back up.
As you are exercising I would definately say you are adding muscle.,this can only be a good thing as muscle increases insulin sensitivity and the bodies need for energy, which inturn makes it easier to slim.
dont worry to much about your actual weight just keep an eye on your measurements, waist, arms, legs etc...