Thanks for the query.
As you are having 28 days cycle ovulation can occur at around 14th day.
fluid can contain spermatozoa
and the sperms can be alive in female genital tract for around 5 to 6 days in ideal circumstances.
So there is possibility of pregnancy
Urine pregnancy tests may not detect early pregnancy sometimes, so you better go for blood test
for pregnancy which will rule out the possibility.