My last period was on the 2nd of may
Well you wouldn't be pregnant yet most likely, conception and implantation take up to 6 days. Plan B is available at the pharmacy without a prescription or notification to your parents and will reduce the likelihood of getting pregnant by about 85%. The sooner you take it, the better it works. You have 72 hrs after sex to take it for it to be effective. There is a good chance - statistical speaking- that you were ovulating and could become pregnant.
If you are going to be sexual active you really must figure out how to protect yourself. Condoms are the only things that prevent STD transmission. And It is a good idea to be on the pill, patch, shot, or ring add backup.
Good luck!