What is it I have on my.. well, skin?

More than a year ago, on one place on my skin (not a very nice one to talk about.. on a ...boob.) appeared some kind of weird thing and I still struggle to get rid of it. At first it was was like a sore that would heal, then come back, then again disappear, then again reappear. It wasn't oozing or anything, at least not too much, even tho it did make cracks go through the sin there even when it was supposedly healed. Not long ago, about a month ago, it became absolutely uncontrollable. We tried to use different lotions and streptotsid and tried to put plasters on to prevent any dirty stuff from coming to it, but it only made things worse! Now lymph oozes out of it non-stop and won't heal one bit. it is also pretty big now... in a diameter of about 5-6 Centimeters (making it about 2 inches). Today I tried to keep it untouched for as long as I could (managed to hold only for an hour, since it's such a place that must always be covered even when one human is around) to maybe allow it to dry, since we always keep either plasters, or just my bra, or napkins on it all the time. Well, the results didn't please me. It kept Oozing to the point drops were on it already and only one of those drops (small ones) dried and nothing more! it was disgustingly all yellow... I really don't know what to do anymore.. I still have yet to go to the doctor, but maybe you guys can at least tell me what this is? Because we are completely clueless...