How to get baby to stop pinching ? *TMI PHOTO*

My daughter is only 4 months old and I know she won't understand if I tell her no but she keeps pinching my breasts when she nurses and it's really frustrating me. She bruises my skin. It hurts so bad. She yanks my nipple in and out of her mouth with my skin on my breasts. It's so painful. How can I discourage this? If I swaddle her she will fight the swaddle and scream and not eat.