Spotting or light period?

I thought/think I started my period on Monday since I started spotting and I did feel some soreness on my lower back and boobs. But I've been spotting/or having a light period since then. Today is Friday and it's the same. Also it's dark brown not the usual red. Should I be worried or is this something normal that can happen just because???? I don't think I'm pregnant but I can't say I'm not until I'm able to take a test after my period is gone. Any idea???