I have thinning hair. I'm only a 29 her old female.

If several doctors told you that your hair loss was genetic, it is probably genetic. Internet is not a substitute for your doctor.  If you have concerns about the depo shot ask your doctor.

In females, hair loss can be due to genetic causes or non- genetic ones as well of which one of the most common ones is called as Telogen Effluvium. It can be due to improper diet which may lead to low Iron levels, or thyroid problems or due to some other hormonal problems. Stress is also a cause for hair fall. So, a proper work up is required to rule out other causes of hair fall in your case and then medical treatment should be done.