i had brain surgery, and now I'm going bald. I'm a woman of 37. What can I do?

There is no particular "cure" for Diffuse Un-Patterned Alopecia. There may be some treatment options but you need to see a doctor for a proper exam first.

If you have nutritional deficiency and it is the only cause of your hair loss, it is possible to reverse the hair loss.  However it would be highly unlikely hair loss in the crown area is due to eating junk food and nutritional deficiency.  

You cannot make your hair grow 5 inches in one week. That is not possible. Hair grows about 1cm a month.

Lasers may cause permanent hair loss. Sometime it may not be permanent. Only time will tell. It can take several months.

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.

Taking "lots of tablets" for hair loss may not be in your best interest. See a doctor for a proper exam and explore treatment options based on your diagnosis with realistic expectations and goals.