Can anyone tell me what's happening?

So I started birth control a month ago and it's been going really well. But I'm around the time I usually get my period and something werid's going on. 
Basically I have times where there's a little bit of blood/bits mixed with my discharge. It happens at least once a day, then will suddenly stop for the rest of the day. It's been happening for the past 3 days and I'm not sure what it is.
Is it just spotting (I've never had any spotting before so I wouldn't know) or am I just having a super light period or could I be pregnant (i heard something about people bleeding a little when they're pregnant, idk I its true or not though)