It sounds really tough for you OP, and hats off to you for managing 4 children!
I have no medical knowledge and I hope the GP continues to investigate with you.
I appreciate that you may already eat really well etc, I am not assuming anything but wanted to add my experience in case it was helpful.
What I will say is that when my children were small, I had many of the same symptoms as well as depression and anxiety. I was constantly feeling ill, aches and pains and bowels and tummy in a terrible state. I was overweight but not obese and I walked a bit but no formal exercise. Plus I drunk too much wine as a coping mechanism.
After a couple of years of this, I decided I needed to sort myself out - I went on antidepressants, stopped drinking completely, cut out UPF and gluten, and now eat a very clean diet. Also started getting more fresh air and more walking and as I started to feel better, I went to a gym with a friend and amazingly got really into it, and I get a huge endorphin hit when I go. I am 4 years into this lifestyle and it has transformed my physical and MH. Obv, if you do have fibromyalgia, exercise is not recommended I think- but for a long time, I simply just went outside more and pottered , sometimes just reading my kindle on a park bench.
If someone had told me the difference changing my lifestyle would have made, I wouldn’t have believed them. I know it isn’t a magic cure, but for me, it has transformed my life.