i have a large lump on my back , its been there for a few years now ,i was told by gp it was a cyst and nothing to worry about so i left it , and forgot about it , today my sister came round and said she could see a black dot on it, so i told her to squeeze it. a yellow, darker than normal pus came out , it was quite solid in form and had a cheesy smell that was really strong. it took over half an hour before it finally stopped . would just like some advice on it please