HELP!!

We just welcomed a new baby girl into our family 3 weeks ago and my 20 month old son is NOT having it. Ever since she was born he is acting out of control. I have to drag him into school as he is screaming down the hallway and hitting me and throwing things (embarrassing to say the least). He also has started throwing food and whining SO much. Every morning is a nightmare bc of how he acts and how he whines. Me and my husband are at our breaking point and welcome any and all advice to help modify his behavior and/or help him feel better. I understand he is going through change but it’s to the point where he acting out is very concerning!