Breast or formula

Hey ladies. I have two kiddos one is almost two and one is 5 days old. I didn’t breast feed my first for very long but I decided to try to exclusively breastfeed my 5 day old. Well here I am at 5 days with scabbed nipples that are very sore and I have to use a nipple shield because my nipples aren’t long enough to stimulate the food of her mouth. It’s been a battles since day one and I’m starting to want to give up at use formula but I’m having so much guilt about it. Any advice?