A runny nose, sore throat and fever up to 103 that eased with Sinarest and paracetamol, then flared again by day four, fits a common viral upper respiratory infection, sometimes triggered by travel and cabin air. The throat pain returning doesn't necessarily mean a new infection, since viral symptoms often dip and spike over several days before settling.
Next Steps
Continue paracetamol for the fever and throat pain, and keep up fluids and warm salt-water gargles. If the fever spikes high again, lasts beyond five days total, or you develop ear pain or breathlessness, see a general physician for an exam and a strep or flu check.
Health Tips
Go in sooner if swallowing becomes difficult, your glands swell, or the fever stops responding to paracetamol.