OK, Dr. Fluther. What could be the cause of this pain in my side?

It is located midway down my ribcage, on the left side. It’s red and swollen, soft to the touch. My husband said the other day it looked like several mosquito bites (which isn’t likely since it’s under my shirt.) Plus it doesn’t itch. Since then it has expanded into one larger, swollen red section. It really hurts to touch it, it gently aches if I don’t touch it, and every so often it will send out these STABBING pains. It’s like some one is stabbing me with a fork! It really hurts. It also seems to be spreading somewhat to the front (under my boob.) They’re separate from the one big one, smaller, but doing the same thing. It kinda sorta looks like poison ivy, but it isn’t.
Last week I had what I assumed was a pulled muscle in that same general area, but that ran down the left side of my back, not down the side.
Have no idea if the two are related.
I have a Dr’s appt on Wed, but I may push them for one tomorrow because this just seems to be getting worse.
Any clue what’s going on guys?