For the past 3 days I've felt sick, been getting head aches, fatigue and abdominal pain but I haven't been sick or had diarrhoea. Is it a stomach virus?

Possibly. A viral gastrointestinal infection is quite likely in view of headache and fatigue. These usually resolve in several days and diarrhea Generally ensues. Treatment is symptomatic with rest,adequate fluid intake,Tylenol (acetaminophen). If diarrhea becomes problematic avoid harsh roughage and take kaopectate. If abdominal pain persists or worsens,if abdominal tenderness,or vomiting develops, get examined by your MD.