I'm at school, go to lunch, drink milk, go back to class, and than go to another test than i fall asleep is it because i'm missing vitamins?

Natural course: Be sure you have enough sleep at night. It is common for people to have what is called alkaline tide or hamburger shift after lunch, and unfortunately so. Proper diet is all we need. I don't believe in vitamin supplementation unless really necessary. The only two used as real vitamins in your system are a and k. The rest are used for the metabolism of food which are present in the foods anyway.