Something Seriously wrong with my nipple?

For about a week or so, my left nipple would hurt if I applied pressure to it, I figured it was just sore. But then a few days ago, I found this little string-like flesh under it, I figured it was a veie or something like that, my nipple still looked the same. Then, last night, If found that it had more than double in size, and you can see a white mark above where the string-like flesh is. It looks like a welt mark. Also, it looks as if it my left nipple is silghtly larger than my right one, which is new. If someone could give me a diognostic, and a cure, that would be great.