depression seeping its way back in, yet again

I am trying to be happy. It's exhausting. It's harder to be fake than to just be sad. At least being sad is real. I am having a bad day today... how do you explain depression and sadness to someone who has never felt it and doesn't understand what you are going through? How am I supposed to feel when my kids best friends moms are happy go lucky and laughing all the time, that I don't mean to be nor want to be a downer mom sometimes... but I was handed a life sentence I wanted no part of.