Recently I lost 15 kg and now it is always cold. Really mostly always. My mother said it is because of my weight loss. Do you think this is right?

Yes, I agree. But also different people do have different tolerances for heat and cold. My wife and I both prefer warm weather over cold weather, and both feel very cold even when others say the weather is nice. But my wife has lost weight as she's gotten older and the cold affects her much more than it did before though.