I used to get that when I pumped exclusively. it is a sign of a clogged duct, although if it's out, then it may be resolved. If you see them frequently, you may be more prone to clogs. Be sure to check your breasts after each session to make sure there are no lumps. If you find lumps, massage and heat may help.
To prevent them, you can try drinking a bit more. You can also make sure you fully empty the breasts each time, and you can try heat and massage before and as you pump or nurse.
By the way, the milk is fine. If your baby were nursing directly, you wouldn't even know it was there.
I breastfeed for 19 months and all i can really tell is that is not normal, it sounds like a infection to me. Does it hurt when you pump? it could be engorgement or plugged duct. I would go to the dr or call your neighborhood LLL. But to increase the production just keep pumping and getting baby to feed on it.