Ive been having slight headaches been tired and feel sick to my stomach and diarrhea. what could be wrong with me?

Infection: Sounds like a viral gastroenteritis. You could try pepto-bismol safely. Should you develop any blood in your diarrhea, or high fevers it is more likely bacterial and you should consider getting seen by a physician.

Viral infection: It could be as simple as a viral infection - common in the fall season. However, 1) if symptoms worsen such as neck stiffness, 2) you experience a rash in your arms and legs, or 3) if you recently received a steroid injection and you are now experiencing these symptoms shortly thereafter, don't hesitate to go to the nearest ER to get evaluated. Otherwise, drink plenty of fluids and rest up.