Yes girls can get periods whilst they are pregnant.
Yes there is enough sperm in his pre ejaculation to get you pregnant, there are even traces of sperm in boys urine. Remember it only takes one to get you pregnant!!
If I were you I would get a test and see if you are pregnant, and in future use contraception because with sex there isnt just a baby to worry about theres .S.T.D.S!! So if u cant be bothered with using condoms, then go for the injection or the pill.