S.O.S. Bleeding days after sex

I need some advice because I’m panicking. I had a sexual encounter on Sunday. My partner was large in size/ girth but I experienced no pain during sex. Everything was fine but come Tuesday I began wiping pink and have been bleeding (like on light period days) ever since. I’m wearing panty liners daily to avoid staining my undies. As for pain, I have none. No pain urinating, no foul smell no discharge just the bleeding and I see it in my pee too. Should I be concerned or perhaps my cycle is changing? I’m not due to start until the 25th of November. Any OB/nurse medical advice is highly welcomed/needed. Do I need to go to the ER? Thanks