I have a flat nipple and baby can't latch on it, I am frustrated, we're both frustrated at this point, I want to breastfeed so bad. He's 4 days old. Any suggestions on what to do?

You can try using a pump to suck it out first prior to feeding, some sites even suggest to ask your husband to suck it out for you (this is kinda too weird though!). But just keep trying. once you and baby are pros at feeding (especially getting used to the nipple that isn't flat), you will find a way to make the flat nipple work.