I stain while using Pinda - do I have anything to worry about?

There is nothing to worry about - this is normal. Mid-cycle spotting at the beginning of the contraceptive adventure is not a bad symptom. Their occurrence is natural and results from the body's habituation to hormones received from the outside. During the first months of contraceptive use, spotting may be irregular and withdrawal bleeding may be scant, or it may not occur at all. as long as you use the tablets every day, without skipping any of the doses, at the same time - there is no reason to worry, the effectiveness will be preserved. For your psychological comfort, you can do a pregnancy test after 10-14 days after intercourse. I encourage you to read: https://www.gdziepolek.pl/artykuly/jakie-leki-oslabiaja-skutecznosc-antykoncepcji https://www.gdziepolek.pl/artykuly/jak-prawidlowo-stosowac-antykoncepcje