What Causes A Mole On The Armpit?

So, I have a mole under my armpit that has changed A LOT recently. I went to the doctor who said there was nothing to worry about. It's not a mole but a wart. Everyone else, including nurses say that it is a mole and needs to be looked at. The doctor did give me a referral to a dermatologist. However, the armpit that the mole is on stinks. My other armpit does not. What does it mean? Could it be a sign of melanoma?