last night i went to my boyfriends house and we decided to go skinny dipping. we were both naked and things began to heat up. he began to rub against my vagina with his penis and it is possible that very little of his penis was inserted for a very short period of time. however i am worried because this was unprotected and being in water makes becoming pregnant easier because there is no air to kill the sperm. but he did not ejaculate inside me. unfortunately im unsure of where in my cycle i stand. I think i should be getting my period in a couple of days. im a teenager and my period isnt an exact 28 days.what are my chances of becoming pregnant. please give me some answers as soon as possible. thanks