guppy clamped fins

I've had this guppy for about a month now and 2 days ago his fins got clamped. I didnt know this wasnt bad so the next day his fins got super clamped. He swims side to side but he still eats and poops normally. He is in a very overcrowded tank. It's a 10 gallon tank with a betta, 4 guppies...