Milk not coming in

Jessica
I'm 6 days postpartum and my milk has still not come in. I've been having to supplement because my little one lost over 10% of her weight. I've been nursing her for as long as she'll nurse up to an hour and if she still seems hungry giving her formula after. Im definitely not making enough to satisfy her. She could nurse for hours on end and still act like she's starving after. I'm getting so discouraged that my milk isn't going to come in. Has anyone else's milk taken a long time to come in and was still able to EBF once it did?