Red And Purple Abcess On Chest. Has Leaked, Why? Clogging, Why? Worry?

Hello,my name is Hannah and im concerned. My mother has a reddish purple lump/abcess on her chest right. above and slightly on the top of her brest . The doctor gave her a cream and the first night it started leaking but just alittle bit and what leaked out was a clearish brown liquid. It only has leaked anything once and now in the center of the lump/ boil/whatever it is a black dot that you can feel,it kind of feels like a splinter poking out of it. The lump has always been tender and sore,but the black dot i think might be clogging up whatever is inside . She has gone to the doctor and they told her she had a low fever and they gave her antibiotics and a cream. but she was very allergic to the antibiotics and had to stop taking them and she now only uses the cream. What do you think this could be? I m really worried for her, so in a expert advice would be amazing. Thank you.