What is this Huge painfull nerve I have on My ?

I routinely do self exams, Two weeks ago I woke up with alot of pain on . I found a huge nerve like cord coming from the side of my upper right goes down and around the nipple area. I scheduled an appointment but its a month away. Has anyone else had this problem. My is still tender and sore especially when I wear a bra or when I try to sleep. Can't seem to find much info on this problem. Can cancer just grow overnight like that?