Your breast and private pain could be a side effect of the Plan B pill.
PLEASE insist that anyone you have intercourse with use a condom AND also make an appointment with Planned Parenthood or your local health department and get started on the pill. Using BOTH a condom and being on the pill will give you protection against STDs and greater protection against unplanned pregnancy.
STDs can cause SO many problems. People emphasize things like HIV/AIDS (and don't get me wrong thats a big one) but overlook things like chlamydia, HPV and other, VERY common STDs that can lead to infertility, cervical cancer and other long term negative effects.
PLEASE USE A CONDOM! Use a condom EVERY time. Until you are in a committed, monogamous relationship (such as marriage-and even then condoms can't hurt...my ONLY brush with an STD was when my 1st husband caught chlamydia from someone he was sleeping with...but I didn't get it because I suspected he was cheating and insisted he use a condom with me).
Try not to worry so much. Plan B has a really good success rate.
Wait until you miss a period and check again to make sure. I'm sure you are not pregnant, but test again to ease your mind.
Good luck!
A pregnancy test will not pick up the pregnancy hormone 3 days after you have had sex. You need to wait at least 2 weeks and then test with first morning urine.
If you don't want to get pregnant please use protection. With the withdrawal method you are playing Russian roulette. If you use a condom it will at least protect you from some STD's also.
Good luck