Litmus paper and nitrazine paper DO the same thing, sort of, but they are not the same. Litmus paper tests acid vs. base, but nitrazine paper shows a change in colour through the range of pHs.... so 6 is different than 7 and 8 is another shade of green.... etc (colour changes from yellow to blue). Litmus paper probably won't tell you what you want to know because you want to know if your pH is above or below 6.5.
I agree with the other ladies, go with your gut feeling
you know your body best.