Help!

Hey everyone! So on NYE (Jan 1 since it was after midnight) my boyfriend and I had sex. He didn’t wear protection but pulled out just in time. Also, my period had just ended earlier that day. When I checked this app, it said I had a 5% chance of pregnancy since I wasn’t in my fertile period.

Well it was just my time of month and it came on time, but was super weird. The first day I had a LOT of dark brownish red blood. The next day was normal looking period blood and a lot. (I usually bleed a lot the first couple days). But the ‘period’ only lasted 4 days. Which mine usually last 6. And it was super weird and off an on.

There are a few factors that may be the reason for this: super stressed at work and taking pain medication for my wisdom teeth since they are coming in.

Also, on the 4th night when I realized my period was funny I went and bought a pregnancy test and it was negative.

Am I just going crazy and over thinking everything? Help!