@Musical_geni if you took them outside of your 3 hour window it takes time to be protected again. Having sex during the time you are unprotected has a chance to ovulate, but it’s not a guarantee. Pregnancy tests are most accurate 21 days. If the result is negative then then you can definitely rule out pregnancy.
It is entirely possible you’re just unwell, it’s that time of year where a lot of people are experiencing different sicknesses.