What Causes Skin Tag With Clear Liquid In It On Areola?

I have a skin tag on my areola. It is about 10mm long. I have had it for about two months. Two days ago I noticed that the top 5mm looked like it had a clear liquid in it (like a blister) Today it is black. I had breast cancer 4 years ago. I went to the specialist two days ago and she didn't mention it. I had in fact forgotten about it so didn't draw her attention to it. The examination was very brief and some what unfocused as I had my one year okd daughter with me. Should I be concerned by this tag?