never happened to me before ?

I have been on my period since Thursday, it's been pretty normal but lighter than usual due to the Plan B that I took two weeks ago. I noticed that there was no blood yesterday so I figured OK my period is over with and I ended up having sex we checked there was no blood but I did feel more dry than usual, now it's almost 5 o'clock the next day and I started to bleed a little bit more so I wanted to know if this was normal it has never happened to me before I guess my period just wasn't over yet but it's weird that no blood came off during sex ???