When a mole starts to bother you suddenly, that invariably means not cancer but minor trauma. I'm sure that when you see the doctor, the dark spot--if it's even still there--will be diagnosed as a small scab from the mole's rubbing on your bra. The needle sensation is also almost certain to be from the rubbing.
Just keep the mole covered so it doesn't run, and don't freak out--just see the doctor for reassurance and you'll be fine!
Best.
Dr. Rockoff