Could hormonal changes in a woman cause a swollen lymph node in left side of chest (above breast, below collar bone) for 2 days now? no fever yet.

NO: This should not be related to a hormonal problem. Usually when a lymph node (if that is what it is) enlarges as a response to infection or inflammation of which there can be many causes. It may not be a lymph node. It could be a cyst or an early abcess. If it persists, it needs to be checked by a doctor.

See your physician.: This is not a typical place for a "lymph node", so the nodule in question could be something else, perhaps a sebaceous cyst, perhaps a tumor. It would be prudent to have it checked by a physician (e.g. Pcp).