"My daughter is 4 years old and doesn't speak..."

Hello.

I have a problem with my daughter 4 years old because she doesn't speak. I mean, in her own way, yes, but sometimes it's impossible to understand her. Says single sentences like "Mom, I want to drink". In addition, while talking to her, she sits and as if she listens, but does not understand, and after a while she bursts into tears for no reason. And her behavior... She can be aggressive. He beats not only his siblings, but also me. After a while, she is like another child - well-behaved as if nothing had happened. He will come, he will hug, but he can also hurt himself. I used to think it was sibling jealousy, but I don't think it's jealousy's fault.

Maybe someone had such a case or has experience with children and will tell me what to do, because I don't know anymore.