What Causes Recurring Pimple In Between And On Breasts?

I have a really large pimple in between my breast and it get to the size of maybe a small marble and it pops it self and then goes down but it will keep coming back within weeks or months, it hurts really bad an now it s moved to making both my breast hurt it use to hurt just where the pimple was, but now it moved to my breasts is it something serious, and when it pops it bleeds and yellow liquid stuff comes out