Hi, i have a really hard pea-sized lump behind my left ear. it's been there for over a week. should i be worried?

It could be a: cyst or even a small hardened lymph node. If not resolving, consider dermatologic eval to determine diagnosis.

Considerations: Is it tender or have you had someone else look at it?Is the skin around it red or is there a "whitehead"?Otherwise if no pain or redness,fever, consider an enlarged lymph node which could be sign of infection somewhere else in the head region or just incidentally enlarged with no significant problems.Have someone,or your doc,take a look at it to make sure it's not an infection.

Could be a cyst: or on infection or a lymph node.........Have your doctor check it out.