Is A Painful Mole On The Armpit Cancerous?

Is a painful mole cancerous I am 35, 135lbs. and disease free except for anxiety. I have a large black mole that has a califlower texture on my underarm. In the past year I have gained 10lbs and my clothes are now tighter. My shirts are rubbing the mole and it feels like it is stinging or just irritated. Could this mean the mole is cancerous or is it just irritated from my clothing. It has not enlarged or changed shape or color.