What can I do? I’m losing my mind

My oldest daughter is 6. She is funny, smart, so kind, and so caring but she is also spoiled. She thinks she can have anything which yes is somewhat our fault also her grandparents. We’re trying to teach her.

I know every kid is like this that screams to not go to bed some nights. It’s very rare it’s this bad but neither of our kids are sleeping through the night, they usually end up in our bed. I’m pregnant with our third so I’m trying to stay awake enough to put them back in their beds but I’m exhausted. So is my husband because he’s been dealing with it every night.

Tonight my 6 year old woke up 30 minutes after going to sleep and pitched a huge fit over having to go back to sleep in her own bed. I’m staying firm and making her but my god the temper tantrum and the begging and crying I had to step out of the room. I go back in and she’s screaming again and I just lost it. I started cussing and telling her how sick I am of her shit. I feel horrible. I feel like all I do is lash out at her. I don’t feel like I even know her anymore because all she does is whine for the things I tell her she can’t have. Like candy all day every day. It’s a constant battle with her. I just don’t know how to fix our relationship.