OP, I felt the same as you for years and years, which thinking back came on after the birth of my DS. Anaemic, depressed, anxious, hair falling out, monstrous fatigue, really heavy periods, weird feeling pulse/heart beat and brain fog/memory problems.
After pushing for years and getting fobbed off with 'oh you've got a young child and a full time job, you're bound to be tired' etc I got a full thyroid function test and was diagnosed with Hashimoto's. Got put on thyroid tablets and thought that was the answer but still went for years and years with not feeling myself, bouts of extreme tiredness, depression getting worse and worse, worsening memory and just a general feeling of something being 'wrong' with me.
Few years later was told to take a high dose of vitamin d (3,000 iu daily) as was deficient in that too, and for a while I felt better, but then back to the same old symptoms.
Then broke a few bones, had a dexa scan (again at my insistence) and found out I had early onset osteoporosis which was blamed on the low vit d.
Still getting anaemic and this was always put down to my heavy periods, but by this point I was taking 200mg ferrous fumerate every day for about two years and still had no iron stores.
Someone randomly mentioned me being a celiac about this time last year, which I thought was nonsense as I'd never had any of the typical celiac tummy type symptoms. I did an online assessment on the celiac society's website and was astounded to find out they thought I might have it. Then fainted a few times on the train to work, so went to the docs and demanded to see a gastroenterologist, has an endoscopy and lo and behold, I am celiac and probably have been for years.
Anyway haven't had any gluten in eight months and feel totally different - my iron levels, b12, vit d have all shot up to where they should be, my periods have calmed down, I'm off my antidepressants, I stay awake past 9pm now, my bone density should be improving and I don't feel like some sinister, hard to pinpoint and explain feeling of being ill is there anymore.
As everyone has said, it could be a lot of things (thyroid, endo etc - autoimmune diseases like celiac and hashimotos like to go hand in hand sadly) but it sounds from my experience like you're not absorbing nutrients properly, and you mentioning some foods making your stomach feel odd (spaghetti for example) sounds alarm bells to me re gluten.
I'd definitely push for ruling any absorption issues out. Leaving it too long has nasty side effects like osteoporosis and broken bones are no fun!!
Hope you get some answers soon. Don't be shy to be insistent - you know yourself better than anyone 