Input needed please. Trying to decide if I should go out and buy a pregnancy test.

Backstory: My period has been very regular and down to the day for the last 6+ months, before it was only off by a little, I was expecting my period on November 9th. So the 7th I had sex unprotected, we’ve been really good at timing things 😬 Well the 9th rolls around and I only have a few small cramps no period. Fast forward to the 19th and I start bleeding, it’s lighter in flow than my period is normally and didn’t last as long either however it was clotty. Over the last week or two I’ve noticed my breasts have become larger and nipples slightly more sensitive. Also my stomach has been throwing random bouts of nausea at me and then just as suddenly they will stop. Is there a chance that I ovulated late and that what I thought was my period was actually implantation bleeding? Cant decide if I should go out and buy a test I’ve been working so many hours. Thank you! Sorry if that was long and slightly tmi?