Your gut and microbiota
Your Colon/large intestine is Full of Bacteria, mostly good.
Your colon is full of beneficial bacteria, and a few nasties. There are 100 trillion bacteria in your colon and 1000 species. It is like a thriving rainforest down there. This is where your feel good neurotransmitters (serotonin, noradrenaline and GABA) are made. If you want to feel good and happy, get your gut right and it will happen.
You may ask "Okay serotonin is produced in the gut and serotonin will releive my depression, but how does that serotonin get into my brain?"
Well, it doesn't actually get into your brain but your gut is connected to your brain by a superhighway called the Vagus nerve. The Vagus nerve basically connects every organ in your body to every other organ.
So more serotonin in your gut = more serotonin in your brain = you feel good.
Fix your gut = Fix your depression.
I know it works because I have done it myself and helped others.