It's a hard adjustment for sure. I work part time now, but I will give you the best pointers and what I learned helped me.
Schedule a bit of downtime. I love my child, but 24/7 is a lot. Since you said you love working, maybe find a bit of time a couple times a month to volunteer for a cause you care about. You will feel like you're doing someting important, and get an all important break.
You will need some mommy friends. To have playdates with or friends that you meet up with occasionally. Adult conversation.
Make a budget. More importantly, set up an amount of free spending money for you every month. When I stopped working, it felt like all the money was H's money. You should still have some fun money (other than grocery/household).
Congrats on the new baby, and on making a big change.