period?

Okay so I'm 18 and I've been on birth control for about 2 months now. 2 days ago I felt like my period had started so I went to the restroom and it was very light pink blood And I guess it wasn't my period because it lasted like that for the past 2 days. It happened last month as well but it only did the light pink blood for a day and the next it was a normal period. This time It's not much blood either but it's been 3 days and there's no change. My boyfriend and I pretty much use only birth control as our protection. Has anybody had the same experience or any advice? I'm pretty worried about this situation.