Brief Answer:
Sebaceus cyst seems most possible.

Detailed Answer:
Hello!

Thank you for the query.

Can you please attach a photo of it? Is it right or left collar bone?

Lump below collar bone can be an enlarged lymph node or any soft tissues lesion including sebaceus cyst or lipoma.
From mentioned lumps, most common lump which can be painful is sebaceus cyst. There should be some redness and swelling present with this condition. Tiny dot on the skin should be also visible in case of sebaceus cyst.
Painful cyst usually indicates an infection. In such case it should be incised and drained.
As this can be also a lymph node, soft tissues ultrasound should be done to rule it out.

The best you can do is to consult general surgeon with this issue.

Hope this will help. Feel free to ask further questions.
Regards.

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