Please don't give up. I can only tell you what I went through and hope it might help you.
I am 45 too (nearly 46) and I have pretty much lost over a decade of enjoying life due to ill health which for the main part was undiagnosed by Doctors.
I was told I was depressed, hormonal, pre-menopausal, agitated, difficult, perhaps suffering with hypochondria, the list goes on. I almost gave up so many times I could only force myself to carry on because of my daughters.
Then a new Doctor did a blood test 2 years ago; hey presto I was diagnosed with HYPOTHYROIDISM, it was severe at the time and caused the Doctor some serious concern (!), as far as the GP is concerned my condition is now 'under control', I disagree, but then why should they care (yes I am bitter about it now and with good reason). Over the last year my health declined to the point where I was unable to walk the length of my house outside, could not always manage to get up the stairs, was effectively thinking that I was about to die. I was REALLY scared and refused to give up, I had to be taken to the Doctors because I couldn't walk very far at all, and used the lift there because I couldn't get up the stairs (I am 5' 2" and at the time weighed 11 stone, so not really big and weight wasn't the cause). I went to the Doctors at least three times a week, they were very fed up with me but still I persisted.
Eventually they agreed to send me to see a Cardiologist on the day I refused to leave.
Result: I have ANGINA.
Apparently high cholesterol is a major cause of Angina and high cholesterol can be connected with HYPOTHYROIDISM, one of the tell tales signs for the Cardiology team was the pain I get in my jaw, so that's worth looking out for by the way.
If left untreated for long enough the hypothyroidism and raised cholesterol can cause heart disease and angina. But check this out with your GP, it's just what I have been told about my condition, it might be different for you.
When I wasn't treated I felt like I was about to die, couldn't remember anything at all, oh the list goes on and on, my family even thought I was perhaps early onset Alzheimers, my memory was that bad (apparently it's the low blood oxygen saturation that causes memory problems). Since my treatment for Angina has started and I also use my Glyceryl Trinitrate spray when need too, I feel like life is worth living again. I am in the process of setting up my own craft business from home, can walk longer distances too. I cant get up the stairs yet at the Dr's, but I will only have to see them now once a month.
So, I am sorry this was such a long reply and I hope it helped you. It's always worth following your instinct and not giving up,