I’m so scared & nervous! HELP!

Over the last couple of months I've been having unprotected sex with my boyfriend, although he's been able to withdraw before cumming. I kinda started to bleed saturday night (the 23) & woke up to it even heavier sunday morning. i woke up today (the 25) and saw the flow was lighter. My period isn't supposed to be due till tomorrow. Neither one of us have any STDs. I also thought implantation bleeding is lighter in color and not as heavy. I read that there might be a possibility that I'd be pregnant, but I also read it could be stress too which I have been for the past week. i know that when having unprotected sex anything is likely to happen. My period doesnt normally come early, although once in a while it does come late. I can’t be pregnant that’s the last thing I need right now. I'd really appreciate any suggestions, I really dont know what to do or who else to ask.