For the past couple of years I have been having trouble with gaining and maintaining weight. I weigh 100 pound and I notice that my arms and legs are way skinnier than before, especially my legs. (I used to weigh 120 pounds). I notice that some of my jeans are even getting a bit bigger. I honestly don't know what to do. Should I work out and try to build muscle mass? I also have an issue with my mood affecting when and how much I eat. If I get too excited, feel too lazy, or too sad, I don't feel like eating. I also have a bad habit of snacking instead of eating meals, which causes me to be more fidgety and burn calories instead of gaining weight. I want to be around 120lbs again, as I feel more secure with more weight on me. Any tips to help me out?