Normal or no?

So my boyfriend and I had sex for the first time a few weeks ago, and this past weekend I started my period. The first day was super heavy and the second day was super light, almost like there was nothing there towards the end of the day. We decided to have sex again the second day of my period considering there was no blood at all. I should be on my 4th day of my period now but it’s like it has completely stopped a few days early. I still a little bit of brown spotting I guess you could say when I pee but otherwise that’s it. I’m still cramping in my lower back/abdomen though. My periods usually last 5-7 days. Is this normal? Like is this just my body adjusting to having sex or should I be concerned? I’m on birth control (have been for about 4 months) and he’s used a condom each time we’ve done it. Thanks!