Hi Irish!
I work P/T but I'm hopefully coming out of work soon to be a SAHM.
The things that helped me when I was on maternity leave was volunteering at my church toddler group, and I took up crossfit. I still do both as I made some lovely friends and get a lot out of them.
What are your hobbies/interests? You could have a look at www.do-it.org and see if there's anything there that tickles your fancy.
Exercise is great for your mood, and achieving little goals (lifting heavier/running further/changing body shape) is great for your confidence. If money is in short supply you could try couch to 5k.
Not trying to shove anything down anyone throat, but I find churches are great communities of people with lots going on. Toddler groups/coffee mornings/food banks etc that you could help at or attend, if that's your thing.
You could visit the sick or elderly,
volunteer to help in an animal shelter, do beach cleans, join the PTA.
But aside from all that what you are doing has such value. Raising the next generation and supporting your family is nothing to be ashamed of. A person's value isn't based on their earning power. You being at home enables your husband to be out at work.
I hope you feel better soon. 