Hello Loubee, and a warm welcome to the forums.
You have 4 young kids and it is a complex and definitely a demanding situation you're in and with your 4 year old being referred to counselling must mean you are taking on this responsibility, especially as you've suffered from PND which can raise it's ugly again, although I'm not qualified to say but know from experience.
The reasons maybe different from last time when you were trying to cope with 'domestic violence' and PND, but this illness has a wide range of reasons and it's still PND, again only mentioning this from experience.
Being a young mum is a 24/7 hour day and how you are feeling can happen at any time, I just wonder whether you can find time to see your doctor when the oldest is at school, I know it's not easy but you also have to look after yourself, so are you able to make some friends where your 7 year old is at school.
Please remember you have many friends here you can talk to.