Is spotting when using Atywia Daily normal?

Hello. This month I started using the first contraception in my life, currently I am on the eighteenth tablet of Atywia Daily of the first pack. Today I observed first a slight abdominal pain, which after a while passed, and a little later brown spots on the underwear. If I didn't take the pills, I would have a day of ovulation in two days. Is such a symptom normal? Could it be, for example, a symptom of pregnancy? I had intermittent intercourse without additional protection a week ago. I use the tablets regularly, I did not happen to miss any.