Four days ago I had a sore throat, fever/ headache, all gone. I now have a runny nose with green mucus/ a slight cough producing green mucus at times?

Green mucus. Sounds like what everyone gets. Drink lots of green tea with lemon and honey. Don't blow nose hard. This material is infected so bag your nasal wipes. If not clear in days, ask your doctor about using Hydro Pulse Nasal/Sinus irrigator to restore nasal cilia function and clear the infection.