Since being off the Pill, I've spotted before my period starts, often for 3 or 4 days, and often with "days off" right before AF. It's really annoying.
Due to the spotting, I was worried about low progesterone too, so I started charting, only to discover that the spotting was starting after 10DPO. So, even if low prog was causing spotting, I still had 10 days that were OK, and I stopped worrying about it. So, charting may answer some of your concerns
I still mark the start of AF as the first day of "proper" flow, rather than the start of spotting. Which, of course, is resulting in LPs varying more than they should- so I don't have it all figured out, either!