Breastfeeding issues

My baby isn’t latching at all. I have tried everything, he’s 13 days old and has been having formula milk and I think he’s used to the feeder nipple, now.

My nipples are also an issue as they are a little flat. When I pump they stick out other wise they are somewhat flat. My milk came in real good in the beginning but now it’s decreasing as the baby isn’t latching.

Any suggestions on what should I do? I have been super worried and extremely guilty. I’d always prefer my babies to be exclusively breastfed but I never knew this would occur.