There is a chance you are pregnant. The pull out method is BS. He still had precum and that def came out during sex even if he pulled out. Precum has A LOT of sperm in it.
About the discharge and tender boobs. It could be pregnancy or it could be side effects of starting bc. In all seriousness...there is usually pink discharge during implantation bleeding (where the egg becomes fertilized by sperm)
Have you taken a pregnancy test or can you get one?
First day of your period shouldn't be your fertile day so it may not have caused a pregnancy. However, the menstrual cycle is unpredictable, so the pull out method is not always effective since it MAY introduce a small amount of ejaculate in the vagina.
Chances are, however, that you aren't pregnant and the symptoms you describe are common to BC pills too.
Also, most symptoms of pregnancy are not manifest so early on