Marcia
A swollen lump under the arm pit may be nothing more than a cyst but if it is growing you need to have a doctor look at it. If you are a woman, it is especially important because breast tissue extends into the armpit and your lump could be cancerous. Don't put this off due to complacency or fear. You need peace of mind. It may be nothing but if it is something it need to be addressed now before it gets bigger.