Flat nipples - how to breastfeed?

Hello mummies! I just delivered bb couple of days ago, and different nurses have been telling me that i cant latch bb well and he doesn't want to suckle because i have flat nipples. This is quite discouraging. Bb has been so sleepy and refuses to latch – he rather sleep and hasnt been drinking formula milk much too. Anyone with similar experiences and tips? Thanks in advance!