I had sex 9/20, got my period 10/18, it lasted 4 days when i wipe there's a light blood could i be pregnant?

Possibly: But unlikely do a pregnancy test to be sure

Unlikely: That you became pregnant, but it's possible you may have picked up a sexually transmitted infection, accounting for your spot bleeding. The only way to be certain is to have a doctor examine you. You could do a home pregnancy test to be sure about pregnancy, but my advice is 2 go 2 your regular doctor for a pelvic exam. That way you can be tested for STDs at the same time and get treated if needed