Painful lump on lip

Beth • Done with it all.
I have this painful lump on my lip. It started as a small blackhead a few weeks ago and now it's a semi - hard spot like lump. It's very painful full to touch and stings. Can anyone tell me what it is? I've had coldsores before but they a bigger and don't tend to hurt. I also have one sexual partner that I've had for over a year and a half so it can't be an sti. Hope someone can help!!!