I had a bout of diarrhea for around two hours after drinking too much coffee. This was around 12-2pm. The diarrhea did not persist and my stomach was feeling better. At around 9:30 I took my birth control pill as usual. It was the second to last active pill. Does having an upset stomach affect the way the birth control pill is absorbed, even if I did not vomit or have diarrhea after taking it? I got my period when I was supposed to but it was slightly lighter than usual, is this normal?