Heavy unexpected bleeding

So today I went to the gym and worked out a little harder than usual. I just had my Nexplanon removed last month and didn’t know when to expect my period. Let’s just say I bled through my leggings and didn’t realize until I got home. I was sweating so much I thought the extra moisture was sweat. Hopefully no one saw but that was pretty embarrassing. Has anything like this happened to anyone else? How did you handle it?