I am on oral birth control for estrogen replacement therapy due to undetectable levels. Should my Dr be rechecking my levels to ensure the right Dose?

Low dose bcp. Taking low does oral contraceptives replaces all the estrogen you need for normal functions. It is unusual for a "23 y.o." to have "low estrogen". Ask your gyn provider about "PCOS" , and ask for his/her reasons why estrogen is apparently "low".