Could I be pregnant

The last time I had sex was on new year’s <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> and I also skipped my period that week but I had missed the first pill of the week so I took two on monday (i usually start on sunday) And I had sex on Tuesday. I had my period when I was supposed to but now I have this like reddish brownish discharge and I’m not sure why. I feel like I’m getting fatter too. That could be just because i haven’t been eating well. I know birth control isn’t 100% effective, also i’m fairly skinny and i’ve heard stories of girls who have stayed the size they were and then suddenly went into labor without knowing they were pregnant. Can anyone give me some advice? Is there a possibility I could be pregnant?