Hi,
Noted your history of headache,
sore throat,
tiredness, warm dry mouth, feeling hot and cold, phlegm that is thick and yellow.
The most probable causes can be as follows:
Pharyngitis with an active bacterial infection.
Sinusitis.
Decongestants can cause dry mouth.
Tiredness indicate infection.
Hence I would advise you the following:
Consult your Doctor and get a referral for an ENT Surgeon if needed.
investigations of blood.
CT scan of sinuses.
Throat swab.
All these will lead to a proper diagnosis and thus treatment.
Till then take steam inhalations.
Anti-inflammatory like Ibuprofen if it suits.
Povidone iodine gargles.
Plenty of warm oral fluids should not be missed.
Take care. Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. T. Chandrakant, ENT & General Surgeon