What Causes Abnormal Menstrual Discharge?

So I got my period you could call it that, on sunday and usually my period would start off with like dark spotting then turn into the regular red blood but then the next days it stayed like that dark color and it wasnt heavy but not super light either. I had sex like 3 weeks prior to this and we were protected. Also I got my period twice in January. One in the very beginning and one at the very end it it didnt last as long. Is there something wrong? Because this period thats like a dark color worries me.