I'm 19, female, 5'8" and 175 pounds. I have no sex drive since I went on birth control for four months over 2 years ago. How do I get sex drive back?

Not uncommon. Great question. It will help many women. It is quite common to sense decreased libido on bcp's as they downregulate your ovaries, estrogen and other sex hormones.Don't worry. You can change your birth control with your ob/gyn; find a new form of non-hormonal birth control like the iud; enhance your libido with topical testosterone or enhance your own libido mentally, physically, spiritually.
Getting mojo back. You are really young to have this problem, but being on oral contraceptives with "fake", synthetic hormones in it can suppress your ovaries, where you make most of your testosterone. You need a testosterone level check, and possibly the administration of bio-identical testosterone in a topical creme or dissolve-under-the-tongue troche or mini-troche. You may also need a different oca. Good luck.