Is fertilization possible in this case?

If intercourse took place at the time of proper use of active pills, then protection against pregnancy at that time was maintained in accordance with the declaration of effectiveness of the manufacturer of contraceptive pills. Pregnancy tests performed after 3 and 3.5 weeks after intercourse speak in favor of the absence of pregnancy. If you feel unwell and this condition persists, it is worth contacting your family doctor. I enclose additional information: https://www.gdziepolek.pl/artykuly/test-ciazowy-jaki-wybrac-i-kiedy-zrobic