My mother had an ingrown toenail on her big toe and let it go for months, even though it was painful. When she finally went to have something done, they found that her toenail had grown down toward the bottom of her toe around both sides of her toenail. So, the pain she felt was awful because with every step down, since her toenail was almost poking through the underneathe bottom of her big toe, it was unbearable pain.
I think you have to cut the sides to prevent this from happening. Or have a doctor do it. Infection would make it so much worse.
Get it checked out.