You are not alone.
Many of us - including me - have been through really serious :end-it-all" depression so we know what you are experiencing, and how people who haven't experienced it have no idea how bloody enervating it is. Getting out of bed is a major acheivement - having a wash and getting dressed - well, might as well try to put a man on the moon! It's like wading through shoulder-high treacle,
This exhaustion coupled with the deep, deep sadness you are suffering will pass, I promise you. You are grieving for what you thought you had and taking your children's pain onto yourself, too. I think your mam is frightened by your depression and doesn't know how to cope.
I'm always so scared about opening up to health professionals about how I really feel in case they judge me as being an unfit mother
I was the same - I was actually terrified that they would put my children into care, so I know exactly where you are coming from, but you do need support. Of course you will get it here, but a face-to-face supported can be very helpful, too.
The Samaritans can offer this, and I think that if you speak to your GP, s/he may be able to suggest or to refer you to support groups, if you don't want further counselling.
Holding you in my heart and my prayers - this is an awful time for you.