What Do I Do?

I have a daughter who just turned 2 in December. She doesn’t have a vocabulary hardly, she’s started to pick up a little bit here and there, but she hardly talks. She doesn’t do well with other kids. She screams at the top of her lungs 24/7. Has done this since birth. She wakes up every night in the middle of the night screaming. Always waking my other children. She’s hardly an affectionate child, but has her moments. She doesn’t listen at all. Like you can look her dead in her face and tell her something or ask her something and she’ll ignore you. Something as simple as “please come here.” And then when you get up she takes off running. I love my child but idk how much more I can handle. I need answers. Why does she behave this way? What can we do? We do not spank, I am a very loving mother, my other children do not behave this way. I’m at a loss. I’m losing more sleep with her than I am my 6 month old. She always been this way, since birth. At first I took it up to “must be her age” and my parents even said it was a phase but we’re all starting to see that this isn’t. Can someone please help? She has an Appt this week so we can discuss this with her new Dr. Her last one never took us seriously. Just said “that’s how children are” but no, as a parent I know something is wrong.