My period is 4 days late, pregnany test negative, sore nipples, white discharge one day, very rarely have irregular periods. i am a 28 cycle generally?

Recheck test soon: I think you can proceed in two ways. It would be perfectly reasonable to see your doctor in next day or two for a breast exam and more detailed blood test to check pregnancy or you can wait a few more days and recheck a home pregnancy test to make sure it is negative- you may still be a bit too early. If there is any doubt, see your doctor.