Brief Answer:
Could be Sinusitis / tonsilar infection

Detailed Answer:
Hello Friend ..
Thanks for your query to Health Care Magic ..

I am Dr .Kingson will help you to know the cause of Left sided headache and Earache that associates with Sore Throat.
The infections of the throat are more likely to affect the ear as there is a connection between the ear and throat through the Eustachian tube.
So I would probably say that Tonsilitis ( You could see tonsil in mirror using tongue depressor and light source) .Your symptoms can be treated with rest, fluids antibiotics and saline gargle; I would suggest warm compresses of ear, pain medications, ear drops to ease Earache .

Also If there is history of blocked nose then Its Left Sinus tract Infection which caused you feel headache . Simple nasal decongestant will do good to clear nasal obstruction.

Drinking plenty of warm water or warm tea with lemon and honey helps to relieve the discomfort caused by the sore throat.

I hope this information is useful.
Thanks & Take Care.

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