Weird AF

So normally my period is about 6 days. This month it was two days early was literally only 3.5 days. It was heavy one day and normally I have 3 heavy days and 3 lighter days. It's almost like clockwork always. So this is so weird to me. Any thoughts? Just a weird cycle? I mean it was bright red so I'm assuming it couldn't be pregnancy? (I know the only way to know that is to test, so I'm not asking for a magical answer) just looking for some insight;