Pregnant. But period ?

So I had unprotected sex in my fertile window three and a half weeks ago and I had a lot or pregnancy symptoms . I took a test the day AF was late and it was a very very faint positive but 3 days later I started bleeding heavy and cramping and I was so nauseous and it was brown and bright red blood . And now a few days later I'm having horrible back pain and slight cramps . Could I still be pregnant ? I'm too scared to get my hopes up and take another test ..