Breast pain/size

My left breast has been a Ton smaller than my right (other than when I first hit puberty), now, it seems like overnight it has literally gotten way bigger, almost to the size of my right. I've been having burning/stinging pain in the left breast for a few weeks now. It all started when I accidentally hit it & it hurt so I looked down at it & I found a lump. It actually was like a huge pimple still under the skin. I poked the lump & some pus came out of it. I squeezed on it (probably shouldn't have done that), & a TON more came out, then blood. It has hurt/burned ever since. The lump went down a good bit within 24 hours of squeezing it. Some remained for about a week & it went down more. Now, it is just a tiny bit still there, I'm just really worried about the pain/stinging/burning. I cannot touch it & it even hurts to wear a bra.

I'm wondering why the sudden change in size as well as what that lump could mean.

I do have a Dr's appt., but it's just going to be a while before I get in and I'm very confused & worried.