Try an over-the-counter hair growth product. There are products made for both men and women that are found to be effective by many people.
Some of the products are hair growth-stimulating shampoos, and others have a more complicated application process that requires you to sit with the product on your head and allow it to work. Do some research to figure out which is right for your needs.
Test the product on one discreet part of your head before applying it to your entire scalp, since you may have an allergy.