I suggest donating your time or skills to helping others in some way. It doesn’t have to be a great endeavor, especially because I am sure nursing and taking care of people is emotionally draining.
I started assistant coaching a local kids’ sports team that had very little funding. Turns out that it was incredibly rewarding to work with kids and watch them grow. I also found friends in other coaches who had similar interests to me. We could always commiserate over complaining about waking up early for practice or certain kids that were difficult, and friendships grew from there.
Maybe kids aren’t your cup of tea. But I have always gotten a seratonin boost from helping other people. That might be an easy place start. Aside from that, maybe a hobby that requires you to interact with others. The first thing that pops into my head is glass blowing, because there is a shop in my town. You can take a class with other people, if you hate it then it wasn’t too expensive of a trial because they have all the equipment. If you like it then you can participate more with the shop. Something along those lines?
Excersice. I know, it sounds trite. But working out has helped me sleep more soundly despite getting less sleep. I have a few weights in my basement and when my kid is sleeping, I go downstairs and lift heavily. Especially leg workouts, your legs are a huge portion of your body and getting those muscles working is great. It usually takes me ~20 minutes to workup a sweat. Before I had a child I used to try cardio for longer periods of time. But I am more satisfied with short, difficult strength workouts.