The "lump" is most likely a skin phenomena. Probably a blocked sweat gland (Sebacious cyst) or a blocked hair follicle. Keep the area clean and wash daily with dial soap and water.
You got screwed on the X-ray but the nurse practitioner felt like he/she had to "do something" to make you feel better. It also jacked up your bill.
Bottom line: Keep an eye on it. If it gets bigger have someone cut it out and be done with it.
u have had a reaction?
what i suggest u do is, go through what you have changed in the week that the lump appeared (new soap, food, new cleaning agent, new deodorant, etc.)
if you isolate the change, you can stop whatever it is (like switch deodorant) and see of the lump goes away.
but im no doctor, this is just my suggestion.
Thanks for you comment Steve, but I haven't changed any products recently.
Get to a hospital IMMEDIATELY! I have an Uncle who discovered a similar lump on his arm. He died.