When does breast milk stop?

When is the breast milk supposed to have finished after birth? I stopped breast feeding 61/2 years ago, yesterday I saw whitish substance from my breasts, and I had my periods last month, im ruling out pregnancy. What can be wrong? If pregnant, when does the colostrum start?

Breast changes and milk. Breast tenderness, and possibly a slight increase in breast size are common signs of early pregnancy. The nipples often become very sensitive and the veins under the skin more noticeable. Many women increase in bra size as their pregnancy progresses (usually after around 20 weeks or so), but others do not notice much of an increase until after the birth and their breast milk comes in (which is temporary for a week or two).

It is possible for a woman to start producing 'colostrum' any time after about 14 to 16 weeks of the pregnancy. Colostrum is the first fluid a woman's breasts produce and is a clear or creamy-yellow substance that is syrupy in consistency. It is possible for some women to hand express colostrum from their nipples during pregnancy, or to slightly leak colostrum occasionally, especially if this is not your first baby. (Be aware that leaking colostrum during pregnancy does not happen for every woman and your milk may not become obviously noticeable until after your baby is born.) If you are leaking colostrum and it is becoming annoying, you may need to wear breast pads inside your bra.
I FOUND THIS ON A WEB SITE I HOPE IT WAS HELPFULL. ( I THOUGHT I BETTER ACTUALLY RESERCH THIS ONE LOL)

Dear sharray,
You must see a doctor ASAP...it may be nothing but any changes such as this can signify a problem. There are certain conditions that are related to these symptoms.
Sue...good luck