why do my nails curve in weird ways?

both my pointer finger nails curve downwards, n my right middle n ring fingernails curve awkwardly on one side, n curve upwards on the other side. i have no underlying health conditions that i know of, nothing to do w lungs at least. i’ve been growing my nails to paint them for about a year and a half now, but this has only been an issue for a few months (btw, they’re stained cause of nail polish pigments, n the nail beds are short cause i was an avid nail biter for a couple years in my youth)