Are you diabetic and taking insulin? Your history is very vague, whatever you shared the concern is not clear,
From what I get there is no chance of conception theorotically if unprotected sex in first three days, but from history if you are on insulin it suggest you have insulin deficiency or resistance and resistance is symptoms of PCOS, please get proper consultation
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Earlier the better, no urgency if fear of pregnancy because that's not possible 👍