I am so sorry you are feeling this way.
Please don't see it as YOU have failed just because some medical treatments haven't been effective.
My answer to when you throw in the towel is NEVER!!!!
When I was 34 I had a life altering brain injury that left me unable to even sit up without fainting, severe head pain and intractable vomiting. I had to crawl around the floor of my home and pee in a bucket because I couldn't get to the toilet.
My quality of life was sub zero and I was completely abandoned by the NHS, told to just go away and spend the rest of my life lying down.
I did seriously consider euthanasia, but two things stopped me - my children, and after extensive research the knowledge that treatment did exist that could give me some quality of life.
I kept on fighting for care, and after 5 years I got a blood patch (privately) that over several months worked to stop the CSF leak so the splitting orthostatic headaches went away, after 6 years I got medication to support my blood pressure and after 7 years and a private online consult with a specialist in syncope, made possible by the pandemic as I could never have travelled to London in person, he wrote to my local hospital recommending a pacemaker, which in conjunction with everything else has been completely transformative.
I am so glad I didn't give up, and although I am still disabled and life is far from perfect, I am truly grateful to be here.
There is hope for you.
You felt well before your hysterectomy so there clearly is a particular hormonal milieu that suits you and can be replicated pharmacologically, if not perfectly then close enough to get you better than where you are now.
The estrogen levels you mention are low, especially for someone in her 40's.
Have you considered oral estradiol? In my experience this is a lot better than patches.
Also there is tibolone. This is a 3 in one oral option which I have seen people do really well with after surgical menopause.
Two other treatments that have really helped during my own journey and which might be relevant for you, are mirtazapine, which I initially used for the severe nausea and vomiting in the first few months after my brain injury when no antiemetic licenced for human use was effective, and which I still use now for sleep, and diazepam for the autonomic storms, PTSD and secondary anxiety that I developed as a result of my circumstances.
Never stop trying to get the help you need. It exists and you deserve it.