I can understand your concern for weight gain. Probably you have a high metabolic rate, thats why you are skinny. If you are prone to anxiety, then you must try to control it by staying calm and cool. Do not bother about what people have to say. Eat well and have small frequent meals if you can't eat much at a time. When your appetite is low, try to have energy dense foods like potatoes, rice, breads, pasta, bananas and if non-vegetarian include mutton, chicken and fish, eggs in your meals. Have full cream milk and curd and cheese . Do not skip any meal and do not stay hungry for long hours otherwise you will feel weak and fatigued. Sleep well at night and avoid taking too much stress. Drink enough fluids like fruit juices, thick fruit milkshakes, add 2-3 teaspoonfuls of whole milk powder to milk. Keep nuts and dried fruits like cashews, peanuts, walnuts, almonds, raisins, pistachios with you. Have them as snacks in between meals. You can also make dried fruit powder by grinding them in a mixer grinder and add it to milkshakes, custards and puddings.

Hope these suggestions will help you in gaining weight and staying healthy and strong.