Sorry to hear about your problem. You are suffering from a sebaceous cyst
, which is nothing but a blocked hair follicle. This can sometimes cause whitish substance to come out through the opening. This is nothing to be scared about and it is certainly not associated with cancer. If you want, it can be removed under local anaesthesia.
The nipple pain is due to the hormonal
changes and it usually occurs 5-7 days before the menstrual periods. It subsides as the periods start.
Hoping for the best.