My smart assed (though, honest) reply is Xanax. I'm mostly optimistic to annoyance but I do have my darker days and that's when they help a ton.
Other than chemical 'cures,' I would say to you that we all go through things day to day, and year to year. If you're going through a true depression, seek professional help because perhaps you need it. If it's just a case of everything kind of coming down on you at once and you're feeling overwhelmed, sometimes it does help to think of what you DO have that is good in your life. Think of the things that make you happy ... sometimes it's something so damn simple but it's important to you. Someone always has it worse off, you know?
For some people, volunteering helps and since you said you do enjoy helping people, maybe that's something to look into. They say exercise helps but if you're truly miserable, hiding out, eating ice cream and watching some good movies may be better suited to you.
I know I always feel better after a massage, too. Honestly, you MUST make time for yourself. I find that is key, at least in my life. Quiet time. You have a child so that's probably not something you get too often but even once a week, give yourself something to look forward to that's just for you.
Always remember, this too shall pass.