Spotting after your period is normal. What is not normal is if you continue to spot for more than a couple of weeks.
What throws off your period would be athletics. Some gymnasts say that when they are extremely physically active, it throws off their period.
If you had sex for the first time, there will be some spotting that could happen. My advice is to just keep an eye on this. It should go away within a few days. If not, if you're a minor living with your mom, you should ask her about this. Hope this helps.