I am new to this forum. I live with PTSD and Major Depression. I empathise with your struggle with constant sadness. it takes it's toll.
I'm wondering if you are currently on medication. I applaud your ability to maintain a working life, and the huge responsibility of raising children whilst managing your illness. Do you have any support at all, to allow time for your necessary self care? Relaxation, walking in nature, classical music, etc? I find they really help as an alternative to vegetating in front of the TV, as I also find myself doing, to switch off my thoughts. Except, there is so much negative sh....t, it does nothing to aid the healing process. You have to be selective in your viewing choices.
I discovered my Depression is linked, in part, to my Hyperthyroidism, and wonder, since your illness is so long standing, whether it might pay to check your Thyroid levels + particularly the thyroid antibodies.
Most depressive symptoms can be linked to Autoimmune Thyroiditis, as the inflammatory cytokines inflame and block neurotransmitters such as Serotonin and Dopamine. Always good to rule out possible causes with a simple blood test.
If your depression is not helped with Psychotherapy or cognitive therapy , it must have a physiological cause.
I wish you well,