Just had a melanoma removed from my back. I couldn't see it, so I didn't know it was there. I was lucky, it was stage ia. At stage iii they start to worry about it spreading to the lymph nodes.
What concerns me about your description is the change in the mole. Go to a dermatologist.
The abcds of melanomas (signs)
a - assymetrical
b - irregular border
c - color, varied
d - diameter (bigger than a pencil eraser)