Your symptoms could be due to a number of things which are difficult to assess on net. It could be due to viral fever, gastroenteritis or stomach flu, acidity, or anxiety and stress. If you are feeling nauseous, then you can take antacid gel. Talk to your parents as discussing your worries often helps. Also, exercise, walking, yoga is therapeutic.
You should see a doctor who can examine you to find the cause. Take care!