What Causes Soft Spot Between Breasts With Pus And Blood?

I'm seventeen years old and i have a soft spot in between the two of my breasts. It's been there for a few years now and it often opens up a little hole in which puss and blood comes out. Also it sometimes get itchy. It goes through different phases, sometimes before it opens back up it turns into a irregular bubble and when the bubble pops it leaves the tiny hole there. When its not open its just a little pink soft spot that never goes away. A while ago my doctor recommended that i use Miconazole Nitrate 2% cream, i used it everyday twice a day and it did not work. Do you know what this could be, the cause of it, or how i could treat it?