him putting his penis inside of you IS SEX! so you must be confused as to what sex is if you think you did not have sex.
what do you think sex is?
youve had 3 periods taken a number of tests and they have all come out negative. YOUR NOT PREGNANT
If this was a few months a go and you still haven't had a positive test it is unlikely that you are pregnant. Also, the fact that you have had three periods since having sex that generally means that you are not pregnant.
I just wanted to add that you did have sex, his penis entered your vagina, you had sex. He doesn't need to finish in order for it to be considered intercourse