How can I treat an ingrown fingernail?!

If there's pus, you need to see a doctor. Whether you want to or not, because it won't get better without antibiotics.
Usually a doctor treats an ingrown by removing the entire nail, or the section which is ingrown. It may or may not grow back normally depending upon how damaged the nail bed is.
If you can't pull the corner of the nail out of your nail bed, you'll need to have a doctor do it. But either way- you have an infection and need antibiotics.
Soak your finger in warm water and epsom salts. This will soften the nail and make it more pliable, possibly easier for you to remove on your own. The epsom salts will also help the infection.
Good luck.