Tender area behind left ear with slightly raised lump on the mastoid bone and dull earache with tenderness in ear canal. Is this dangerous/serious?

Mastoiditis. You need to be seen and examined, preferably by an ENT doctor. This could be very severe and dangerous and you should go asap. Good luck and hope this improves quickly.

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Rock hard, pea sized non tender non movable bump over mastoid bone behind left ear. Been there for 3 months does not change in size? Concern?

Follow. Likely a safe lymph node or if non mobile a small bone. It is tiny and non mobile and does not change. A US may be able to define it further but I'd doesn't sound bad. All the best. Read more...