Period confusion

So after what I thought may be a BFP test I started lightly spotting mostly when I wiped (maybe tmi, sorry!) and that went on for about a day and a half and now the flow is getting heavier but I'm so confused - WHAT do I say is my period start date?! The day that I had light bleeding/spotting or the day it became heavier?! Any opinions/advice would be great..I know I probably sound kinda dumb asking. Ijust want to make sure I have it right since I am TTC.