It is possible. many girls actually break their hymen doing other things than having sex. Tampons fingering and even exercises like gymnastics can break it. It is possible it has been torn. Don't worry, you're still a virgin.
No, stress actually delays a period, but four days early isn't early and is just a regular cycle. No woman's cycle is perfect especially at younger ages, so getting it four day early is nothing unusual.
Birth control should not affect sex itself. If you have pain there during sex, it is most likely caused by something else like an infection or lack of lubricant. If it continues, talk to your doctor.