I am so sorry about the loss of your sweet mom. I have also suffered from depression for most of my adult life, as has my sister. Needless to say my father's death has us both working 24/7 not to slide into complete despair. I am on medication but often feel like it is totally ineffective.
The loss of your mom would have been hard enough without all the other major changes like the house sale, moving and relationships altered. That's a lot for anyone, even without the depression. If you did not seek out some form of grief counseling at the time your mother died (and even if you did, really), that might be an option to explore. Some weeks it is the only part of my existence where I feel sane.
Anyway, you definitely are not alone....some of us have different circumstances of loss, but the crushing weight of grief seems to be a universal thing for those of us who really loved someone, then lost them.
I hope that you are having an okay day.