As the swelling is movable,Cancer can be ruled out.It is also not from Collar bone as the bony diseases are fixed.
It can be Lipoma
,swelling arising from fat cells.Another possibility is a infective lesion,which is can cause pain.
Please take an Antibiotic and anti inflammatory drug .If the swelling does not subside, Consult your surgeon and get the correct diagnosis and treatment.
Cancer can be ruled out by Fine needle aspiration cytology(FNAC) of the swelling.
Wish you good health