Hi. I just gave birth to my second 3weeks ago. Experienced the same thing as you when i came back from the hospital. You need to have patience and explain to your firstborn why you have to spend more time with your second child. Let him understand that baby is still young and needs help. I know its unavoidable, but try not scold or beat your firstborn if he doesnt listen to you. He is just trying to seek your attention. Make it known to him that papamama still loves him. Alternate care between you and your partner. Make sure you spend time with your firstborn as well.
hes being jealous that the center of attention is no longer his. Maybe you can try remind or tell him that you love him still or let him try to bond with his sibling.