Alright, you are 101 pound and your Body Mass Index (BMI) is 18. The normal range starts from 18.5. So you are only slightly underweight. It's really not a matter of concern because with age you will develop fat in your body. Not that bad an idea to stay slim. Make sure you get a healthy diet and your weight doesn't fall below this. What do you mean by loosing weight? Do you mean you were something like 50kg 1 month ago and now you are 46 kg. If that's the case, it could be a matter of concern. Stress may be playing its role in it. As I said, eat a lot of nutritious food and not necessarily the junk ones. Eat those food that contain a high amount of calory. Do some physical activities and keep your mind relaxed, a little bit of meditation may help.
For stress, I would say, you have to take what life gives you having made sure you have given your maximum effort. What has to happen will happen. There is no point worrying about it. Be honest to yourself and you don't have to be afraid of or worry about anything.
Don't worry too much about losing weight and looking fresh and all those stuffs. You may have lost some of the glamor becuase you have lost some weight. No problem, eat a lot of nutritious food, drink plenty of water, and you will start looking as good as before. At the end of the day, it's down to the person you are than how you look. I have a similar problem. When I leave for my university at morning, I look very glamorous but after coming back to home at evening I look very tired and it requires a good 2 hours rest for me to get back all the glamor! So make sure you are getting enough rest and more importantly sleeping enough. Generally, an average adult requires 8 hours of night sleep. Are you getting that?