Any ideas?

So first I am on the depo shot so I do not get my periods except when it’s close to when I’m due for my next shot. But weirdly every couple mornings I’ve been waking up at like 4 in the morning to me having to go to the bathroom and clean up because I started my period. But the period only lasts for a very short amount of time and it’s not that much blood, but it’s not spotting. By the time I wake up at my Normal time (6:30) it had already stopped way before that. I tried googling (I know never google)😂... but I didn’t find anything. I am sexually active, but have not had sex since the end of December. I’m not sure if that info will help or not.