I have low iron saturation & low iron, all other bloodwork is normal. gi issues have been ruled out via colonoscopy and endoscopy. anything else i should ask for? waiting to hear back if a bone marrow biopsy is next. have headaches & fatigue?

You don't mention whether you're anemic. If your iron binding capacity is elevated, this proves iron deficiency. In your age bracket blood loss from menstrual bleeding & not taking iron supplements would be the most like cause of it. I'd try taking good doses of iron supplements and checking labs in a month. At this time, I don't see what useful info would be obtained from a bone marrow biopsy.

Why is bone marrow indicated if other lab results are normal except low iron and iron saturation? Why were endoscopic studies done if you are not anemic?