So then, you have low bone density, are premenopausal, have a malabsorption problem, have had a nontraumatic fracture and are a runner.
Lots of red flags. I do hope you can get some doctor to followup with testing to determine the cause of your low bone density. It may very well be that during your bone forming years, you didn't absorb enough calcium to reach your peak bone mass. It's not that you're losing, it's that you never gained. One scenario.
At this point, if I were you, I would research the ISCD and NOF websites (
www.iscd.org and
www.nof.org ) for all the information I could get. I would continue with the calcium and Vit D......and.....I would stop running. Running is a risky choice if the bone density is low. Power walking would be a better option.
It's possible, at your age, that you could still amass some bone density. Keep in mind that as you approach and go through menopause, you can lose up to 20% of what you have now. Also being pregnant and breast feeding will deplete you bone mass - at least temporarily.
Having had one fracture puts you at twice the risk of having another. I would ask my primary doc or orthopedic to order some physical therapy for body mechanics and ADL's (Activities of Daily Living) to reduce your chance of another fracture.
At this point, there's not much we know or can do about premenopausal osteoporosis unless there's an underlying cause that can be addressed. All you can do is what you're doing and not take chances.
I hope you find a good doctor, stay upright and healthy and have as many children as you want