Is it possible to have period like bleeding after conceiving?

So last month, I had unprotected sex and he came in me. 3 days later I started bleeding and obviously assumed it was my period. I then started getting tons of symptoms that I would associate with pregnancy so I took a test that was negative. I figured I was just freaking out for no reason so I forgot about it. I'm now 3 days late this month and my period is always spot on. Is it a possibility to get pregnant and bleed like that a few days after?

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