Hi, approximately how long does it take for a swollen lymph node (on armpit) to go back to normal? thanks

A couple of weeks: When a lymph node get swollen it is most of the time related to an infectious process. It is the way your body fights infection, so they usually should go away after the illness resolves anywhere between a few days to a couple of weeks or so.

2-3 weeks: An enlarged lymphnode should resolve in 2-3 weeks. If node persists or gets larger, see your family doctor asap.

Apocrine: I have a feeling that more than likely it is an inflamed apocrine gland in the armpit, rather than a lymph node. Avoid friction or trauma, apply moist warm compresses and apply an antimicrobial cream. It should resolve soon.