15 month old driving me NUTS

I have no idea what's wrong with her, she is constantly whining, crying, and throwing tantrums ALL DAY. It's non stop, I don't have a moment that I can think of where she wasn't crying. I'm at my wits end. I have a newborn who cries WAY less than this girl. I put her in her crib just to cry alone right now because I'm about to pull my hair out. According to my wonder weeks app she's supposed to be at her most well behaved, well she's not. She's upset all day, it's her permanent mood.