Tell your Mum and get her to take you to the doctors as soon as possible - its probably nothing to worry about but safest to check
There's multiple things it could be. 1 in every 8 people have a third breast, and it's commonly found in the armpit. Either way, just get it checked.
That sounds more like an issue with your lymph nodes.... Get to a doctor and have it checked. .. Please
Extremely unlikely. Check with a doctor though.
Get yourself seen by the doctor. Never hurts to get checked out.
It's most likely just a swollen lymph gland but get it checked out by a doctor as a matter of urgency. If it's serious (doubt it is), you need to get it sorted quickly.
Don't freak out.. It could just be normal. But get it checked just to be sure
A lump on your arm should be checked out. Is it on the left arm itself or under the left arm... deep under the arm pit..? There are lymph nodes under there and they do swell at times... with an infection like a cold or flue...
Please see a real doctor and not depend on anything else online.