Discharge problem

I had sex the first time a couple days after my period. Everything was fine. I got my period on time abs everything was fine. Couple days later my discharge was a light brown color and I have some spotting. My mom doesn't know I lost my virginty. And I don't want to tell her. I read some things about it.. It said it could be from smoking cigarettes, which I do. So I'm stopping that. I just don't know what to think. And the guy doesn't have any stds or anything bad. I also went to the bathroom after having sex, so i don't know what could be wrong.