I'm not sure whether it's helpful OP but I'll tell you my experience with persistent and severe headaches which I'd been suffering from for a couple of years. I was convinced it was peri-menopause as I'd also been getting night sweats.
Painkillers had mixed results-the most effective was the ibuprofen with lysine but sometimes they wouldn't touch it. I felt sick and dizzy, had constant brain fog.
I tried various HRT all of which made the headaches worse. Blood test results showed my thyroid function was normal and no other deficiencies.
I had my eyes tested and had new glasses even though there was only a slight change in my prescription and I even had a mouth guard made by the dentist as I thought I may be grinding my teeth at night. Still no joy.
Like you, leaning forward made it worse and I found in fitness classes I couldn't do any moves that involves jumping as if felt like my head was going to explode.
Then on one of my multiple visits to the GP I saw a young female trainee doctor who gave me a very thorough investigation and realized something didn't add up so immediately sent me to the hospital for a CT scan. They found a brain tumor 
I spent a week in hospital and after a biopsy eventually diagnosed me with a large but benign pituitary tumor which I've just had surgically removed. I'll also need to have radiotherapy in the next couple of months.
The stats on pituitary tumors are quite shocking-apparently 1 in 10 people will have them during their lives. Many are tiny and won't cause issues or if they do they will affect hormone levels but some will need to be removed surgically.
So if you take anything from my story please get yourself a CT scan. Ask to see a different GP for a second opinion, hopefully a female one. In my experience male (often older) GPs are dismissive of women's pain and discomfort, particularly when it involves something as, in their view, trivial like headaches.
Hope you get some answers 