i get these all the time, legit, do this and it'll cure the next day:
1) soak your feet in hot/warmer water with a little salt
2) soak em for about 10-15 minutes
3) your feet will be pruny as hell which is a good thing
4) the toe with the ingrown nail will be much softer and less irritable, start to just pull the skin away from the nail and the puss will slowly ooze out
5) keep doing this until the inflammation subsides
6) get a sharp mini-scissor-like nail clipper and cut the side of the nail
your nail should grow back fine afterwards