I have been sick with what I think is influenza flu virus since last week. On Tuesday, I had a head ache and sore throat. On Wednesday evening, I developed a fever which lasted until Friday (mostly low grade 99 -100) I now have congestion and am coughing. I don't know if I am contagious and still felt tired so I didn't go to work today. When am I safe to go back to work and not be contagious?