Last month i had sex and after i had slight bleeding directly after. I got my period 2 weeks after

Then i had last week i had sex and no bleeding after. But last night i had sex and there was slight bleeding again.

This has never happened before and i googled what it could be and they said it could be a sign of a STD but i have no pain, no bumps, no itching, no discharge, or odd scent.

What could this be?

Please help!