I have an upset stomach, an on and off headache, nausea, stuffy nose, and my whole body feels very weak and sore.

Common cold. You probably have a cold. Try drinking a lot of plain water- 2 or 3 glasses and take some Tylenol (acetaminophen) or Motrin for the headache. Get some rest and you will likely feel better in a few hours. Good luck and feel better!