Hi Anya - I'm by no means a doctor, but it sounds like you may have had a boil. It's almost like a pimple, because when popped it can produce a chunky off-colored discharge. Also a boil can be quite tender and painful, as it is almost like a lump in the way that it's a hard round abscess. The abscess, aside from being tender, can often be red and warm. Boils are infections that can take months to fester, and often antibiotics don't really work on them unless they are of the anti-bacterial kind such as Levaquin. often boils just need time to heal on their own, to go through the cycle - and if it was popped or burst, you're closer to it healing, as long as the infection/discharge is all gone. if there is still a small lump left, that means it's not quite healed. But I would definitely consult with your doctor. He can probably give you something to help clear it up & double check that the spot is all clear by doing a mammo or ultrasound.
i've had boils in the past and have popped them with a steralized needle, and I will tell you some nasty strange looking things have come out of them - mostly yellowish in color, sometimes hard sometimes gooey. I hope that this turns out to be something minor and that you can set your mind at ease with your doctor's help.
Good luck to you and keep in touch - let us know if it was indeed something more or if you have more questions.
thanks!
Angi