Movable small lump on collar bone. normal lymph node or a sign of something?

Probably normal: May be a small lymph node reacting to some local inflammation, but without examining it impossible to be sure. The location, the fact that it is mobile, and the absence of other symptoms suggests this is nothing to worry about, but should it get larger, hard to the touch, fixed to underlying tissue, other symptoms develop, more appear, it becomes tender and painful, see a doctor.