Dear OP, I've suffered severe depression, low mood, anxiety and insomnia.
These are all symptoms of past loss, maltreatment, abuse (physically or psychological) of some sort, emotional deprivation/neglect, lack of good enough parenting. It could also be a death in the past that you didn't grieve properly. It could be so many things, but it's mainly related to a loss or trauma, especially if suffered in early childhood or infancy.
What really helped in my case was to understand the losses I didn't grieve in the past. My father emigrated when I was a child so I lost him at the age of three even if he didn't die.
It also helped me to understand the relationship with my mother. When I realised how undermothered I was as a child and teenager, it was no surprise at all I suffered from depression later in life.
Once you become aware of your own losses, you can transform them into something better, something healthier.
It's important to set boundaries with the people around you, even if this means low contact or no contact with your family or friends. It's a long journey, but we can all be healed with lots of self care and love that we can give to ourselves if nobody around us is ready to give us right now.
Parenting is also a great healer as by parenting another human being in the same way that we wished we would have been cared for, we heal our own wounds and move forward.
Depression and anxiety is the way our bodies and minds tell us that there is an injury in our souls, that there are emotions that were repressed or neglected. And this is a good thing as they prompt us to heal those wounds, and become aware of who we really are.