Implantation or af?

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16 DPO and I thought I had gotten af on 14 DPO but only bled for 2.5 days, very light, with some brown, not even enough to fill a tampon. I had some cramping and acne this past week. I tested negative today, is there still a chance I could be pregnant? Or is af just very light this month? Typically my periods are 5-7 days & are heavier that’s why it’s odd this month. Anyone else experience this? TIA