Wow - there's so much going on and I really don't know what you could start on, but so far you've mentioned:
- difficult, abusive childhood
- lack of support from DH
- lack of sleep
- social isolation
- no free time
- inadequate support from GP
- depression & anxiety.
That's a LOT to deal with. Any one of those can be mood altering.
But you still need to be aware of the kids & their needs,
Short term - can you book a hotel for a night, and just get some sleep/quiet. Talk to DH, get him onboard with you having a break. He should be doing 50% of the parenting outside of work hours.
Set up a space where you can safely leave DS alone so that you can just walk off if you need to. Go sit outside for a cup of tea, or make his room safe so that at night you can leave him there. I used to let DD sleep on the floor of the hallway rather than get up to her, because then she could self-settle rather than me getting up several times.
Medium term - go back to GP. Describe your symptoms, lack of sleep, depression, anxiety, and ask for med review and referral for counselling.
Try to block out some time each week for you to have quiet time, eg DH takes the kids swimming, you have an hour at home alone to do nothing. If DH is under similar stress, then do the same for him another day.
Find some books that might help you to think through these problems.
Long term - get counselling. Talk through the kind of parenting you had, and how it is affecting your ability to parent.