Toddler acting out with new baby

My son just turned 21 months and we brought his baby sister home about 3 weeks ago. He is having a very difficult time during this transition and I’m not sure what to do. I am doing all of the things, encouraging him to help, praising good behavior, spending a lot of one on one time but he is still throwing fits, hitting, kicking, screaming, trying to go in her swing, (we bought him his own special chair when we noticed it was an issue but he doesn’t care for it). He is also trying to hit the baby whenever she starts crying which is really nerve wracking. He’s not just acting out about the baby he’s also just doing things to get attention like throwing things, hitting our dogs etc. He is so used to it just being him and I because my husband works a lot and he has always been a handful but he’s been sweet. I feel like I don’t recognize him and I know he’s frustrated but I don’t know how to make him happy or feel better about the baby. My husbands back to work now and I feel like I’m failing both kids because I can’t give either the attention they deserve and I feel like I’m drowning.

Has anyone else gone through this with 2 under 2? Send help 😞