This thread actually made me cry, it's heartbreaking to think of so many people who are struggling and the guilt of that regret probably eats away at people as much as the regret does.
I don't regret my DS, but I did throughout the first year of his life. I sobbed to DH that we'd made a mistake, I was consumed with worry and anxiety, I said I hated my baby, I wanted to kill myself it was so bad. It turns out I had crippling PND. I was signed off work for 2mths and given 6mths on Anti-Ds with 3-4weekly reviews from a wonderful and understanding GP.
I'm now a different person, I still find it hard work but that little boy is the absolute light of my life, I love him so much I adore him. I never ever regret him for a second after spending an entire year feeling like that. But I have one child OP, and a husband, and really good family.
I say this genuinely - you're amazing!!! You have FOUR children, on your own, no support, if they're fed and clean you're doing a bloody good job. Please see your GP and chat to him, whether the answer is Home Start, Gingerbread, Counselling, using a Volunteer service (ring your local Children's Services Early Help, there's tons of Volunteers who could support you), or possibly medication if it is PND. Just take each day as it comes, it's ok to regret but also it is what it is and you have the children now, so time to find a way to be happy. Wishing you luck x