I'm having pain on left side of my neck and a red lump on my left tonsil difficulty swallowing headache, and sore throat what is it?

Infection...: Til proven otherwise. Could be strep, viral, other. See md, get diagnosis and rx. Untreated strep can lead to other problems.

Infected tonsil: This could be a simple viral infection but if the pain and tonsillar inflammation worsens an exam by your md along with a throat culture is recommended. With only 1 tonsil involved, entities such as a herpes infection or early tonsillar abscess are possibilities.