What can I use for osteopenia if I don't have a doctor?

Supplementation. You need calcium and vitamin d for osteopenia. There are many over the counter options. The costco brand also very good.
Calcium and D. But how do you know you have osteopenia without a doctor? Calcium, vitamin d, weight bearing and balance exercises will prevent fractures; but depending on your other risk factors for fracture, you may need prescription medication, and you will need follow-up. At least see your primary or your gyn.