Bleeding after sex?

The last two times i had sex while cleaning up i noticed blood on my wipes and i kept thinking im bout to start my period but days later no period

*Blood in very minimal and does not continue after clean up*

The sex was NOT painful and i was wet.

I just did my womans checkup last week plus some STD testing and everything is normal

My period is like 30 days late but test are negative so i dont think its that.

What could this be??