Thanks for query,
You have used saliva kit to detect period of ovulation & done intercourse in fertile period but still the pregnancy
test shows negative result because you have not reached the process of fertilisation of ovum.
For pregnancy the ovum gets fertilised by sperms.It is a complex process as it is not certain that if ovum & sperm meets each other it always fertilise.Many sperms penetrates in side vagina but few of them reached up to ovum & very few of them succeeded to fertilise ovum.
So don't loose hope & take another chance as This will happen every month.