Hay, it's so stressful na 'yan talaga, the waiting and the guessing game, I know the feeling! Based sa timeline mo, it does sound like it could be implantation bleeding dahil light at tapos quick lang compared sa normal period, pero honestly kailangan mo talaga mag-test ulit in a few days or check with your OB kasi sometimes the hCG levels are just not detectable yet kahit may pregnancy na, especially if you're not sure pa ng exact DPO mo. A few of us moms lang dito sa community tried testing multiple times kasi ang first test was negative pero positive pa rin later, kaya don't lose hope yet but it's best to get a proper check-up nalang para sure.