Make sure you are eating plenty of carbs everyday. Here is a good bar that I always keep in my desk at work and have for a snack whenever I get hungery. It is filling and good for you:
http://www.jigsawhealth.com/products/jigsaw-bars.html
You need to see your Dr. It sounds like you might be malnutritioned. I would not recommend you work out till you find out why you get weak at night and from your extra curicular activities. You are WAY to thin. Get help
well if there is nothing medically wrong with u then u need to eat high calorie foods. U said your diet is good...well maybe it is too good. As far as doing workout for biceps and shoulders...forget about it. U need to do major lifts like squats and deadlifts to add weight too your whole body. U will never gain muscle if all u do is isolation type movements. U can gain a lot of muscle from just squats and deadlifts. Biceps curls will not cut it. A person can add a lot of size and strength too their whole body from just deadlifts alone. Also major lifts like that will increase your appetite so u can eat a lot more. How many calories do u eat a day? Probably not enough. Stop wasting time on bicep curls and shoulder workouts if your trying to gain weight.