I had a staph infection. It doesnt look like that. it creates crater wounds, ulcers. holes. Anyway. they lance it to drain out the pus, which is causing the inflammation and pain, and contains a large number of the dead infectious agent and your immune cells that died fighting it.
It has to go somewhere, and out of your body is the best possible place. So when you lance it and drain it, you are removing the remnants of the infection, so it does not return. And yes, its going to be sore for a few days. they cut into an inflammed area of skin, that's gonna be unpleasant.
I could explain in detail if you want, but you really don't. the short of it is, they lance it because if they don't, it may not heal and it may kill you by spreading to your blood and other parts of your body. And honestly when they lance an infection, that's the end of the infection. Almost always. If not theyll put you on anti-biotics.
Calm down. Everything is likely going to be fine. Even in the very worst case, you have doctors on it and you will get treated early enough to treat any complications.
You can trust me. I study microbiology in college (6th year) so I know what I'm talking about.